Chapter 7: Neoplasia Flashcards

Question

TABLE - Comparison between benign and malignant tumors

Answer 1

Comparison between a benign tumor of the myometrium (leiomyoma) and a malignant tumor of the same origin (leiomyosarcoma).

Answer 2

**1. Pleomorphism** - variation in size and shape **2. Abnormal nuclear morphology** - Usually the nucleus is disproportionately large for the cell, causing high N:C ratio, shape is variable and often irregular, chromatin is coarsely clumped and distributed around the membrane or more darkly stained than normal (hyperchromatic) **3. Mitoses** - Many cells are in mitosis in poorly differentiated neoplasms, (high proliferative activity). The presence of mitoses does not necessarily indicate malignancy. However, very frequent, or atypical/bizzare mitotic figures are a more important feature. **4. Loss of polarity** - Orientation of cells is disturbed - sheets or large masses of tumor cells grow in an anarchic, disorganized fashion **5.** **Other changes** - Many malignant and some benign tumors may develop large central areas of ischemic necrosis due to insufficient vascular stroma.

Answer 3

Development of a cancer through stepwise acquisition of complementary mutations. The order in which various driver mutations occur in initiated precursor cells is not known and may vary from tumor to tumor.

Answer 4

* Metaplasia -* replacement of one type of cell with another type; nearly always found in association with tissue damage, repair, and regeneration (e.g. gastroesophageal reflux damages esophageal squamous epithelium --\> replacement by glandular (gastric/intestinal) epithelium more resistant to acid) * Dysplasia* - Disordered growth; usually in epithelial cells; loss in uniformity and architectural orientation (e.g. squamous cells losing the tall to flattened differentiation, and all appearing basilar) **When dysplastic changes are marked and involve the full thickness of the epithelium, but the lesion does not penetrate the basement membrane, it is considered a pre-neoplastic neoplasm, and is referred to as *carcinoma in situ*. Once tumors breach the BM, tumor is invasive. It does not always lead to cancer.** Often seen adjacent to invasive carcinoma, or in long-term cig smokers, it precedes cancer formation. It often occurs in metaplastic epithelium, but not all metaplastic epithelium is dysplastic.

Answer 5

Tumor evolution. Evolution of a renal cell carcinoma (left panel) and Darwin’s finches (right panel). The renal cell carcinoma evolutionary tree is based on genetic comparisons drawn from sequencing of DNA obtained from different tumor sites; the finch evolutionary tree was surmised by Darwin based on morphologic comparisons of different species of finches on the Galapagos Islands.

Answer 6

Hallmarks of cancer.

Answer 7

**The growth of cancers is accompanied by progressive infiltration, invasion, and destruction of the surrounding tissue, whereas nearly all benign tumors grow as cohesive, expansile masses that remain localized to their site of origin, and lack the capacity to infiltrate, invade, or metastasized to distant sites.** Benign tumors often contain a fibrous capsule, separating them from surrounding tissue, thus are easily excisable (exceptions - hemangiomas are unencapsulated). Malignant tumors are poorly demarcated from surrounding tissue **Next to the development of metastases, invasiveness is the most reliable feature that differentiates cancers from benign tumors.**

Answer 8

Growth factor signaling pathways in cancer. Growth factor receptors, RAS, PI3K, MYC, and D cyclins are oncoproteins that are activated by mutations in various cancers. GAPs apply brakes to RAS activation, and PTEN serves the same function for PI3K.

Answer 9

**Metastasis is defined by the spread of a tumor to sites that are physically discontinuous with the primary tumor, and unequivocally marks a tumor as malignant, as by definition, benign tumors do not metastasize.** All malignant tumors can metastasize; due to innate invasiveness, they can penetrate into blood vessels, lymphatics, and body cavities, through which they can spread. Some cancers metastasize very infrequently (e.g. gliomas, basal cell carcinomas of skin). Likelihood ofmetastasizing correlates with lack of differentiation, aggressive local invasion, rapid growth, and large size; WITH MANY EXCEPTIONS

Answer 10

**1.** **Seeding of body cavities and surfaces** - Occurs when neoplasm penetrates into open cavitary spaces (usually peritoneal, can be any); more common in epithelial neoplasms; coats body cavitary surfaces with heavy cancerous glaze; mucus-secreting appendiceal/ovarian carcinomas can fill cavity with a gelatinous neoplastic mass called *pseudomyxoma peritonei* * *2. Lymphatic spread** - **Transport through lymphatics is the most common pathway for the initial dissemination of carcinomas;** sarcomas may use this route too. * *A sentinel lymph node is defined as the first node in a regional lymphatic basin that receives lymph flow from the primary tumor, and can be biopsied to assess presence or absence of metastatic lesion.** **3. Hematogenous spread -** Typical of sarcomas, also seen with carcinomas. Veins have thinner walls and are more easily penetrated, but arterial involvement can happen at AV shunts or pulmonary capillary beds. Liver and lungs are most frequent first sites of hematogenous spread because of portal and pulmonary circulation.

Answer 11

The chromosomal translocation and associated oncogenes in Burkitt lymphoma and chronic myelogenous leukemia.

Answer 12

1. Environmental factors 2. Age 3. Acquired predisposing conditions 4. Genetic Predisposition

Answer 13

**Lthough both genetic and environmental factors contribute to the development of cancer, environmental influences appear to be the dominant risk factor for most cancers.** This is evidenced by the wide geographic variation in specific types of cancer. **Infectious agents**: 15% of all cancers worldwide caused by infectious agents (HPV - cervical carcinoma, EBV - lymphoma) **Smoking:** Cig smoking is the single most important environmental factor causing premature death in the US (larynx, mouth, pharynx, esophagus, pancreas, bladder, **lung** cancers) **Alcohol consumption Diet:**specifics unknown, but important factor **Obesity**: 52-62% higher incidence of cancer than normies **Reproductive history:** little is known **Environmental carcinogens**: UV rays, smog, arsenic in water, medications (methotrexate), asbestos

Answer 14

**Age has an important influence on the likelihood of being afflicted with cancer.** Most carcinomas occur later in life (\> 55 years) Cancer is the main cause of death in women 40-79, and men 60-79. Lower incidence after 80, because cancer patients do not live that long. Cancer accounts for \> 10% of deaths in children under 15yo in US. They get different types (small round blue cell tumors (neuroblastoma, Wilms tumor, retinoblastoma, acute leukemias, rhabdomyosarcoma)

Answer 15

**Acquired conditions that predispose to cancer can be divided into chronic inflammations, precursor lesions, and immunodeficiency states.** **1. Chronic inflammation**: usually carcinomas, but also mesothelioma and several types of lymphoma. Chronic inflammation leads to tissue repair and an increase in number of tissue stem cells., which are susceptible to neoplastic transformation. Immune cells involved in inflammation produce genotoxic ROS and inflammatory mediators that promote cell survival in the face of DNA damage. Chronic inflam leads to metaplasia, so cells are more able to survive ongoing insult. **2. Precursor lesions: localized morphologic changes associated with a high risk of cancer.** May arise in the setting of chronic inflammation and metaplasia (e.g. Barrett esophagus - gastric/colonic metaplasia in esophageal mucosa with gastric reflex; squamous metaplasia of bronchial mucosa with smoking). Others are noninflammatory hyperplasias (e.g. endometrial hyperplasia with sustained estrogen stimulation; leukoplakia: thickening of squamous epithelium in oral cavity, penis, vulva, may lead to SCC) Last group is benign neoplasms at risk for malignant transformation (colonic villous adenoma progresses to cancer in 50% of untreated cases) **3. Immunodeficiency states and cancer**: Immunodeficient patients, especially with T-cell deficits have increased risk for oncogenic virus-inducing cancers (lymphomas, certain carcinomas, rare sarcomas) **4. Genetic predisposition:** Some families have cancer as an inherited trait, usually due to mutations in tumor suppression gene. There is a complex interaction between genetic and nongenetic factors. Breast cancer has a strong hereditary component, but also is influenced by reproductive history.. Inherited variations (polymorphisms) of enzymes that metabolize procarcinogens to active carcinogenic forms can influence cancer susceptibility (cytochrome P-450 enzymes)

Answer 16

Pathogenesis of retinoblastoma. Two mutations of the RB locus on chromosome 13q14 lead to neoplastic proliferation of the retinal cells. In the sporadic form, both RB mutations in the tumor-founding retinal cell are acquired. In the familial form, all somatic cells inherit one mutated copy of RB gene from a carrier parent, and as a result only one additional RB mutation in a retinal cell is required for complete loss of RB function.

Answer 17

The role of RB in regulating the G1-S checkpoint of the cell cycle. Hypophosphorylated RB in complex with the E2F transcription factors binds to DNA, recruits chromatin-remodeling factors (histone deacetylases and histone methyltransferases), and inhibits transcription of genes whose products are required for the S phase of the cell cycle. When RB is phosphorylated by the cyclin D-CDK4, cyclin D-CDK6, and cyclin E-CDK2 complexes, it releases E2F. The latter then activates transcription of S-phase genes. The phosphorylation of RB is inhibited by cyclin-dependent kinase inhibitors, because they inactivate cyclin-CDK complexes. Virtually all cancer cells show dysregulation of the G1-S checkpoint as a result of mutation in one of four genes that regulate the phosphorylation of RB; these genes are RB, CDK4, the genes encoding cyclin D proteins, and CDKN2A (p16). TGF-β, transforming growth factor-β.

Answer 18

**1. Nonlethal genetic damage lies at the heart of carcinogenesis**. Initial damage may be environmental (viruses, chemicals, endogenous metabolites), inherited, or spontaneous and random **2. A tumor is formed by the clonal expansion of a single precursor cell that has incurred enetic damage (i.e. tumors are clonal).** All cells of the tumor have the same set of mutations present at the moment of transformation. Identified by DNA sequencing (point mutations) or chromosomal analyses (chromosomal translocations and copy number changes) * *3. Four classes of normal regulatory genes - the growth promoting proto-oncogenes, the growth-inhibiting tumor suppressor genes, genes that regulate programmed cell death (apoptosis), and genes involved in DNA repair** **- are the principal targets of cancer-causing mutations.** (1) Mutations in proto-oncogenes--\> "gain-of-function" --\> can transform cells when heterozygous (2) Mutations in tumor suppressor genes --\> "loss-of-function" --\> both alleles must be damaged for transformation. Exception: haploinsufficiency- reduces activity of protein enough to release brakes on cell proliferation/survival (3) Apoptosis-regulating gene mutations result in less death, enhanced survival; can be gain-of-function for genes whose products suppress apoptosis or loss-of-function for genes whose products promote apoptosis (4) Mutations in DNA repair genes: Loss-of-function mutations impair cell ability to recognize and repair nonlethal genetic damage --\> affected cells acquire mutations at an accelerated rate (*mutator phenotype*, marked by *genomic instability*) **4. Carcinogenesis results from the accumulation of complementary mutations in a stepwise fashion over time. Malignant neoplasms have several phenotypic alterations known as *cancer hallmarks* (excessive growth, local invasiveness, distant mets)** **5. Mutations that contribute to teh development of the malignant phenotype are referred to as *driver mutations*.** The *initiating mutation* is teh first driver starting a cell on the path to malignancy, and is present in all cells of the cancer. "Initiated" cell acquires numerous further driver mutations, which all contribute to development of cancer. **6. Loss-of-function mutations in genesthat maintain genomic integrity appear to be a common early step on teh road to malignancy, particularly in solid tumors.** These mutations lead to increased likelihood of acquiring driver mutations, and increased frequency of mutations that have no phenotypic consequence, *passenger mutations*.

Answer 19

The role of p53 in maintaining the integrity of the genome. Activation of normal p53 by DNA-damaging agents or by hypoxia leads to cell cycle arrest in G1 and induction of DNA repair by transcriptional upregulation of the cyclin-dependent kinase inhibitor CDKN1A (encoding the cyclin-dependent kinase inhibitor p21) and the GADD45 genes. Successful repair of DNA allows cells to proceed with the cell cycle; if DNA repair fails, p53 triggers either apoptosis or senescence. In cells with loss or mutations of the p53 gene, DNA damage does not induce cell cycle arrest or DNA repair, and genetically damaged cells proliferate, giving rise eventually to malignant neoplasms.

Answer 20

The role of APC in regulating the stability and function of β-catenin. APC and β-catenin are components of the WNT signaling pathway. A, In resting colonic epithelial cells (not exposed to WNT), β-catenin forms a macromolecular complex containing the APC protein. This complex leads to the destruction of β-catenin, and intracellular levels of β-catenin are low. B, When normal colonic epithelial cells are stimulated by WNT molecules, the destruction complex is deactivated, β-catenin degradation does not occur, and cytoplasmic levels increase. β-catenin translocates to the nucleus, where it binds to TCF, a transcription factor that activates genes involved in cell cycle progression. C, When APC is mutated or absent, as frequently occurs in colonic polyps and cancers, the destruction of β-catenin cannot occur. β-catenin translocates to the nucleus and coactivates genes that promote entry into the cell cycle, and cells behave as if they are under constant stimulation by the WNT pathway.

Answer 21

Metabolism and cell growth. Quiescent cells rely mainly on the Krebs cycle for ATP production; if starved, autophagy (self-eating) is induced to provide a source of fuel. When stimulated by growth factors, normal cells markedly upregulate glucose and glutamine uptake, which provide carbon sources for synthesis of nucleotides, proteins, and lipids. In cancers, oncogenic mutations involving growth factor signaling pathways and other key factors such as MYC deregulate these metabolic pathways, an alteration known as the Warburg effect.

Answer 22

By the time tumors come to clinical attention (usually 1 gram, 10⁹ cells), has undergone a minimum of 30 cell doublings (likely a substantial underestimation). Tumors become more aggressive over time (i.e. *tumor progression*). **Selection of the fittest can explain not only the natural history of cancer, but also changes in tumor behavior following therapy.** **In addition to DNA mutations, epigenetic aberrations also contribute to malignant properties:** DNA methylation silences gene expression, histone modification can enhance or dampen gene expression

Answer 23

Intrinsic and extrinsic pathways of apoptosis and mechanisms used by tumor cells to evade cell death. (1) Loss of p53, leading to reduced function of pro-apoptotic factors such as BAX. (2) Reduced egress of cytochrome c from mitochondria as a result of upregulation of anti-apoptotic factors such as BCL2, BCL-XL, and MCL-1. (3) Loss of apoptotic peptidase activating factor 1 (APAF1). (4) Upregulation of inhibitors of apoptosis (IAP). (5) Reduced CD95 level. (6) Inactivation of death-induced signaling complex. FADD, Fas-associated via death domain.

Answer 24

Escape of cells from senescence and mitotic catastrophe caused by telomere shortening. Replication of somatic cells, which do not express telomerase, leads to shortened telomeres. In the presence of competent checkpoints, cells undergo arrest and enter nonreplicative senescence. In the absence of checkpoints, DNA repair pathways, such as the nonhomologous end-joining (NHEJ) pathway are inappropriately activated, leading to the formation of dicentric chromosomes. At mitosis the dicentric chromosomes are pulled apart, generating random double-stranded breaks, which then activate DNA-repair pathways, leading to the random association of double-stranded ends and the formation, again, of dicentric chromosomes. Cells undergo numerous rounds of this bridge-fusion-breakage cycle, which generates massive chromosomal instability and numerous mutations. If cells fail to reexpress telomerase, they eventually undergo mitotic catastrophe and death. Reexpression of telomerase allows the cells to escape the bridge-fusion-breakage cycle, thus promoting their survival and tumorigenesis.

Answer 25

Origins of cells with self-renewing capacity in cancer. Cancer stem cells can arise from transformed tissue stem cells (e.g., hematopoietic stem cells in chronic myelogenous leukemia, CML) with intrinsic “stemness” or from proliferating cells that acquire a mutation that confers “stemness” (e.g., granulocyte progenitors in acute promyelocytic leukemia). In both instances, the cancer stem cells undergo asymmetric cell divisions that give rise to committed progenitors that proliferate more rapidly than the cancer stem cells; as a result, most of the malignant cells in both tumors lack self-renewing capacity.

Answer 26

**1. Self-sufficiency in growth signals -** usually due to oncogene activation **2. Insensitivity to growth-inhibitory signals -** Usually because of inactivation of tumor suppressor genes **3. Altered cellular metabolism -** (i.e. Warburg effect: tumor cells switch to aerobic glycolysis, enabling macromolecule and organelle synthesis **4. Evasion of apoptosis** **5. Limitless replicative potential (immortality) -** helps tumor cells avoid cellular senescence and mitotic catastrophe **6. Sustained angiogenesis** **7. Ability to invade and metastasize -** Due to intrinsic properties of tumor cells and signals initiated by tissue response **8. Ability to evade the host immune response**

Answer 27

The metastatic cascade. Sequential steps involved in the hematogenous spread of a tumor.

Answer 28

Sequence of events in the invasion of epithelial basement membranes by tumor cells. Tumor cells detach from each other because of reduced adhesiveness and attract inflammatory cells. Proteases secreted from tumor cells and inflammatory cells degrade the basement membrane. Binding of tumor cells to proteolytically generated binding sites and tumor cell migration follow.

Answer 29

**1. Genomic instability** **2. Tumor-associated inflammation** These enable cellular transformation and tumor progression

Answer 30

**1. Oncogene: gene that promotes autonomous cell growth in cancer cells** **2. Proto-oncogene: unmutated cellular counterparts of oncogenes** **3. Oncoprotein: Mutated protein resembling the normal products of proto-oncogenes, whose activity does not depend on external signals** **Oncogenes are created by mutations in proto-oncogenes and encode oncoproteins that have the ability to promote cell growth in the absence of normal growth-promoting signals**

Answer 31

1. Binding of a growth factor to its receptor 2. Transient and limited activation of growth factor receptor, which activates several cytoplasmic signal-tranducing proteins 3. Transmission of the transduced signal to the nucleus via additional cytoplasmic effector proteins and second messengers or by a cascade of signal transduction molecules 4. Induction and activation of nuclear regulatory factors that initiate DNA transcription 5. Expression of factors that promote entry and progression of the cell into the cell cycle, ultimately resulting in cell division 6. Parallel changes in other genes that support cell survival and metabolic alterations needed for optimal growth

Answer 32

1. Tyrosine kinase pathway 2. G protein-coupled pathway 3. JAK/STAT pathway 4. WNt pathway 5. Notch pathway 6. Hedgehog pathway 7. TGF-b/SMAD pathway 8. NF-kB pathway **Tyrosine kinase pathways are the most frequently mutated in human neoplasms**

Answer 33

**As a result of this constitutive activity, pro-growth oncoproteins endow cells with self-sufficiency in growth**

Answer 34

Autocrine loop: some cancer cells can synthesize the same growth factors to which they're responsive (i.e. glioblastomas express PDGF and PDGF receptor tyrosine kinases)

Answer 35

**1. ERBB1:** encodes epidermal growth factor receptor (EGFR) which get point mutations related to cancers (i.e. lung adenocarcinoma). These mutations result in constitutive EGFR tyrosine kinase activation **2. ERBB2:** encodes HER2 which is amplified, rather than point mutated, in breast carcinoma. Leads to overexpression of HER2 receptor and constitutive TK activation **3. Gene rearrangements**: Activate other receptor tyrosine kinases (i.e. ALK). A deletion in chromosome 5 fuses ALK gene with EML4 gene in lung adenocarcinomas

Answer 36

RAS MAPK cascade and PI3K / AKT pathway

Answer 37

**Point mutations of the RAS family** These are present in 15-20% of all human tumors. Expressed in much higher rates in specific tumors 90% of pancreatic adenocarcinomas and cholangiocarcinomas 50% of colon, endometrial, thyroid cancer 30% of lung adenocarcinomas, myeloid leukemias

Answer 38

1. Part of a family of membrane-associated small G proteins that bind GTP, GDP 2. They normally flip back and forth between excited signal-transmitting state (bound to GTP) and a quiescent state (bound to GDP) 3. When GFs stimulate TK receptor, GTP binds and activates RAS, which stimulates MAPK and PI3K/AKT pathways 4. These result in phosphorylation and activation of numerous molecules promoting rapid cell growth 5. RAS activation is transient due to intrinsic GTPase activity, accelerated by GTPase-activating proteins (GAPs) **Several distinct RAS point mutations have been found that markedly reduce GAP activity**

Answer 39

* *Mutations in BRAF** 1. Detected in close to 100% of hairy cell leukemias, \> 60% of melanomas, 80% of benign nevi 2. BRAF is a serine/threonine protein kinase that sits at the top of a cascade of other serine/threonine kinases of the MAPK family 3. Activating mutations in BRAF stimulate downstream kinases and activate transcription factors * *Mutations in PI3K family** 1. Very common in certain cancers 2. Normally, like BRAF, PI3K activates a cascade of serine/threonine kinases (i.e. AKT) (a. ) AKT has many substrates i. mTOR - a sensor of cellular nutrient status, is activated by AKT to stimulate protein and lipid synthesis ii. BAD - a pro-apoptotic protein that is inactivated by AKT, enhancing cell survival iii. FOXO transcription factors - promote apoptosis, and are negatively regulated by AKT 3. PI3K is negatively regulated by an important "braking factor" - PTEN 4. All factors mentioned can be mutated to contribute to cancer, but **PI3K and PTEN** are most frequently mutated.

Answer 40

1. These often occur as chromosomal translocations or rearrangements that create fusion genes encoding constitutively active tyrosine kinases (e. g. ABL tyrosine kinase translocation and fusion with BCR gene resulting in constitutively active, oncogene BCR-ABL tyrosine kinase) This mechanisminvolved in CML and some ALLs, and specific, low toxicity treatment has been very successful, a good example of *oncogene addiction-* tumor cells are highly dependent on activity of one or more oncogenes. 2. Nonreceptor TKs can be activated by point mutations that decrease inhibitory domains (e.g. JAK/STAT pathway induces mitogenesis. Point mutation in JAK2 are highly associated with essential thrombocytosis, polycythemia vera, primary myelofibrosis

Answer 41

The ultimate consequence of deregulated mitogenic signaling pathways is inappropriate and continuous stimulation of nuclear transcription factors that drive growth-promoting genes. Transcription factor mutations in TFs that regulate pro-growth genes and cyclin expression can lead to growth autonomy and cancer Examples: **MYC,** MYB, JUN, FOS, REL

Answer 42

1. MYC proto-oncogene expressed in all cells, and is an immediate/early response gene, which is rapidly and transiently induced by RAS/MAPK signaling following GF stimulation 2. MYC protein concentrations are tightly controlled at transcription, ,translation, stability levels, and all pathways that regulate growth impinge on MYC. 3. MYC has very broad activities, including: (1) **MYC activates the expression of many genes that are involved in cell growth** i. Some MYC target D cyclin genes, involved in cell cycle progression ii. MYC upregulates rRNA gene expression and rRNA processing, enhancing capability for protein synthesis iii. MYC upregulates genes (glycolytic enzymes, glutamine metabolism enzymes) , resulting in Warburg effect (2) **MYC upregulates expression of telomerase** (3) **MYC is one of a handful of TFs that can act together to reprogram somatic cells into pluripotent cells** 3. MYC can be deregulated in a variety of ways (1) Genetic alterations in MYC gene (e.g. MYC translocations in Burkitt lymphoma, MYC amplification in breast, colon, ung carcinomas) (2) Oncogenic mutations in upstream signaling pathways can lead to elevated MYC protein levels (e.g. constitutive RAS/MAPK signaling (many cancers), Notch signaling (several hematologic cancers), Hedgehog signaling (medulloblastoma), and Wnt signaling (colon carcinoma))

Answer 43

1. Progression of cells through the cell cycle is orchestrated by CDKs, which are activated by binding to cyclins. CDKIs (inhibitors) exert negative control over the cell cycle 2. **There are two main cell cycle checkpoints; one at the G1/S transition and one at the G2/M transition, each of which is tightly regulated by a balance of growth promoting and growth suppressing factors, as well as sensors of DNA damage.** (1) Defects in the G1/S checkpoint are most important in cancer, as they lead to dysregulated growth and a mutator phenotype. The major cancer-associated mutations affecting the G1/S checkpoint are in two broad classes: a. **Gain-of-function mutations in D cyclin genes and CDK4, oncogenes that promote G1/S progression** (Cyclins D1, D2, D3 can get translocation or amplification mutations. CDK4 amplification occurs in several cancers. b. **Loss-of-function mutations in tumor suppressor genes that inhibit G1/S progression** (CDKIs frequently mutated (e.g. p16 mutations in melanoma-prone people; acquired p16 inactivation in pancreatic carcinomas, glioblastomas, others)

Answer 44

**growth inhibition**

Answer 45

- Two mutations (hits), involving both alleles of RB at chromosome locus 13q14, are required to produce retinoblastoma - In familial cases, children inherit one defective RB copy and one normal copy. Retinoblastoma develops when the normal RB allele is mutated in retinoblasts due to a spontaneous somatic mutation; this is virtually inevitable - In sporadic cases, both normal RB alleles must undergo somatic mutation in the same retinoblast - very low probability In general, familial cancers involving any tumor suppressor gene mutations follow this pattern; risk of cancer is inherited in autosomal dominant fashion, and tumors require a second hit in the normal allele for cancer to manifest.

Answer 46

RB and p53 They cause quiescence or permanent cell cycle arrest (oncogene-induced senescence)

Answer 47

**RB, a key negative regulator of the G1/S cell cycle transition, is directly or indirectly inactivated in most human cancers.** RB controls cell differentiation; it is active and hypophosphorylated in quiescent cells, and inactive and hyperphosphorylated in cells passing through G1/S transition. Two ways RB function may be compromised: (1) Loss-of-function mutations involving both RB alleles (2) Shift from active to inactive state by gain-of-function mutations that upregulate CDK/cyclin D, E activity (CDK4/D, CDK6/D, CDK2/E) OR loss-of-function mutations that inhibit CDK inhibitors **Loss of normal cell cycle control is central to malignant transformation and at least one of four key regulators of the cell cycle (p16/INK4a, cyclin D, CDK4, RB) is dysregulated in the vast majority of cancers.**

Answer 48

**TP53, a tumor suppressor gene that regulates cell cycle progression, DNA repair, cellular senescence, and apoptosis, is the most frequently mutated gene in human cancers.** Like RB, many tumors without TP53 mutations have other mutations affecting proteins that regulate p53 function (e.g. MDM2 amplifications, which normally degrades p53 protein) p53 protein is undetectable in normal cells. In stressed cells, p53 is released from inhibitory effects of MDM2 via 2 mechanisms: (1) *DNA damage and hypoxia*: ataxia-telangiectasia mutated (ATM) and ataxia-telangiectasia and Rad3 related (ATR) proteins are initiators of p53 activation (2) *Oncogenic stress*: Oncoprotein activation (e.g. RAS) leads to sustained signalign through MAPK and PI3K/AKT pathways --\> increased expression of p14/ARF, which binds MDM2 and displaces p53 * *Once activated, p53 thwarts neoplastic transformation by inducing transient cell cycle arrest, permanent senescence, or apoptosis**. (1) **Transient p53-induced cell cycle arrest:** Occurs late in G1 phase, caused by p53-dependent transcription of CDKN1A gene, which encodes CDKI p21, which inhibits CDK4/D cyclin, keeping RB activated. p53 also induces GADD45 to enhance DNA repair (2) **p53-induced senescence:** Permanent cell cycle arrest, may be due to epigenetic changes causing heterochromatin at key loci. (3) **p53-induced apoptosis**: ultimate protective mechanism against neoplastic transformation. p53 directs BAX and PUMA (pro-apoptotic genes) **With loss of p53 function, DNA damage goes unrepaired, driver mutations accumulate in oncogenes, and the cell marches blindly along a dangerous path leading to malignant transformation.**

Answer 49

**Even in the presence of ample oxygen, cancer cells demonstrate a distinctive form of cellular metabolism characterized by high levels of glucose uptake and increased conversion of glucose to lactose (fermentation) via the glycolytic pathway (i.e. the Warburg effect)**. **Aerobic glycolysis provides rapidly dividing tumor cells with metabolic intermediates that are needed for synthesis of cellular components, whereas mitochondrial oxidative phosphorylation does not.** * *Metabolic reprogramming is produced by signaling cascades downstream of growth factor receptors, the same pathways that are deregulated by mutations in oncogenes and tumor suppressor genes:** (1) **PI3K/AKT signaling**: upregulates glucose transporters and glycolytic enzymes, promotes shunting of mitochondrial intermediates leading to lipid synthesis, and stimulates protein synthesis (2) **Receptor tyrosine kinase activity**: phosphorylate pyruvate kinase, inhibiting it, and leading to a build up of glycolytic intermediates (3) **MYC:** upregulated by pro-growth pathways, MYC transcription factor supports anabolic metabolism and cell growth by upregulating glycolytic enzymes and glutaminase ***Autophagy:*** may help or hurt tumor cells

Answer 50

**Accumulation of neoplastic cells may result not only from activation of growth-promoting oncogenes or inactivation of growth-suppressing tumor suppressor genes, but also from mutations in the genes that regulate apoptosis.** **The intrinsic (mitochondrial) pathway of apoptosis is most frequently disabled in cancer.**

Answer 51

**All cancers contain cells that are immortal and have limitless replicative potential due to three critical factors:** **1. Evasion of senescence:** Senescence is associated with upregulation of p53 and Ink4a/p16 which maintain RB in a hypophosphorylated state, promoting cell cycle arrest. RB-dependent G1/S checkpoint disrupted in all cancers. **2. Evasion of mitotic crisis:** Mitotic crisis is attributed to shortening of telomeres. If cells in this crisis reactivate telomerase, they can restore telomeres and survive. **3. Self-renewal:** Each time a stem cell divides, at least one of the two daughter cells remains a stem cell. (in symmetric division, both daughters are stem cells).

Answer 52

**Even if a solid tumor possesses all of the genetic aberrations that are required for malignant transformation, it cannot enlarge beyond 1-2 mm diameter unless it can induce angiogenesis.** Most tumors cannot induce angiogenesis early on, and remain small or in situ until an *angiogenic switch* occurs. Balance of angiogenic / anti-angiogenic factors influenced by: (1) Lack of O2 stabilizes HIF1a, which activates VEGF and bFGF (2) Mutations in tumor suppressors and oncogenes promote angiogenesis (e.g. p53 can stimulate antiangiogenic molecules, thrombospondin-1, and repress VEGF) (3) Transcription of VEGF influenced by RAS-MAP kinase signals and gain-of-function mutations in RAS or MYC

Answer 53

**Invasion and metastasis are the results of complex interactions between cancer cells and normal stroma and are the major causes of cancer-related morbidity and mortality.** Metastatic cascade is divided into two phases: 1. *Invasion of extracellular matrix*: (1) Loosening up of tumor cell-tumor cell interactions: **Dissociation of cancer cells from one another is often the result of alterations in intercellular adhesion molecules and is the first step in the process of invasion.** Loss of E-cadherin function may mediate this process. (2) Degradation of ECM: **Degradation of basement membrane and interstitial connective tissue is the second step of invasion.** This is done by elaboration of proteolytic enzymes (MMPs, cathepsin D, urokinase plasminogen activator) (3) Attachment to novel ECM components (4) Migration and invasion of tumor cells: **Locomotion is the final step of invasion, propelling tumor cells through the degraded basement membranes and zones of matrix proteolysis.** *2. Vascular dissemination and homing of tumor cells*: Tumor cells aggregate in clumps within circulation due to homotypic adhesion and heterotypic adhesion with blood cells, mainly platelets.CD44 adhesion molecule expressed on normal T lymphs helps tumor clumps migrate to lymphoid tissue (solid tumors often express CD44). **The site at which circulating tumor cells leave the capillaries to form secondary deposits is related to the anatomic location and vascular drainage of the primary tumor and tropism of particular tumors for specific tissues.** Tropism related to the following: (1) Adhesion molecules with specific ligands in organs (2) Chemokines (e.g. breast cancer cells expressing chemokine receptors CXCR4, CCR7) (3) target tissue may be a nonpermissive environment

Answer 54

Several competing theories proposed to explain how metastatic phenotype arises: 1. *clonal evolution model*: As mutations accumulate in genetically unstable cancer cells, a rare subset of subclones acquires a pattern of gene expression that is permissive for metastasis steps 2. Subset of breast cancers may have a '*metastasis signature'*, a gene expression causing prediliction for metastasis 3. Metastatic signature may be necessary but also additional mutations (above two combined) 4. Capacity for metastasis may involve characterstics of microenvironment such as stromal components and angiogenesis Possible metastasis oncogenes: SNAIL, TWIST - encode transcription factors that promote epithelial-to-mesenchymal transition (EMT)

Answer 55

"New growth" a.k.a. neoplasm Abnormal mass of tissue, the growth of which exceeds and is uncoordinated with that of normal tissues and persists in the same excesive manner after cessation of the stimuli which evoked the change. Composed of parenchyma (neoplastic cells) and stroma (fibrovascular support tissue with immune cells)

Answer 56

A tumor's production of abundant collagenous stroma - may cause scirrhous (stony hard) tissue

Answer 57

**A tumor is said to be *benign* when its gross and microscopic appearances are considered relatively innocent, implying that it will remain localized, will not spread to other sites, and is amenbable to local surgical remo****val.** While the patient usually survives, benign tumors can cause significant morbidity, and may be fatal.

Answer 58

**Benign tumors** Benign tumor suffix -oma (e.g. fibroma, chondroma) mesenchymal tumors follow this rule, epithelial benign tumors are more complex Benign epithelial tumor from galnds -adenoma (renal, adrenal, hepatic, etc.). These may or may not form glandular structures. Benign epithelial tumors with warty projections -papilloma Benign eipthelial tumors forming large cystic masses -cystadenoma *Polyp* - when a neoplasm (benign or malignant) makes a macroscopic projection above a mucosal surface (e.g. colon, stomach) **Malignant tumors** *Cancer -* Malignant tumor. **These can invade and destroy adjacent structures, and spread to distant sites (metastasize) to cause death.** Malignant tumor of solid mesenchymal tissue -sarcoma (e.g. fibrosarcoma, chondrosarcoma) Malignant tumor from blood-forming cells -leukemia, lymphomas Malignant neoplasm of epithelial cell origin (from any of the three germ layers) - carcinomas Malignant epithelial tumor from glands -adenocarcinoma (e.g. renal cell adenocarcinoma) ***Mixed tumor*** - Neoplasm (benign or malignant) that contains epithelial and mesenchymal components, due to divergent differentiation of a single neoplastic clone (e.g. mixed tumor of the salivary gland, mixed canine mammary tumor) - these are far rarer than simple tumors * Teratoma* (Exceedingly rare) - Contains recognizable mature or immature cells or tissues belonging to more than one germ cell layer (sometimes all three). Originates from totipotential germ cells which are normally present in ovary/testis and can differentiate into any cell type in the adult body (e.g. ovarian cystic teratoma a.k.a. dermoid cyst - may contain sebaceous glands or teeth...) * Hamartoma-* disorganized, benign masses of cells indigenous to the involved site * Choriostoma* - heterotopic rest o cells (e.g. normal pancreatic tissue in stomach, intestines) - no clinical significance

Answer 59

Colonic polyp. A, An aedonmatous (glandular) polyp is projecting into the colonic lumen and is attached to the mucosa by a distinct stalk. B, Gross appearance of several colonic polyps.

Answer 60

This mixed tumor of the parotid gland contains epithelial cells forming ducts and myxoid stroma that resemble cartilage.

Answer 61

A, Gross appearance of an opened cystic teratoma of the ovary. Note the presence of hair, sebaceous material, and tooth. B, A microscopic view of a similar tumor shows skin, sebaceous glands, fat cells, and a tract of neural tissue (arrow).

Answer 62

Leiomyoma of the uterus. This benign, well-differentiated tumor contains interlacing bundles of neoplastic smooth muscle cells that are virtually identical in appearance to normal smooth muscle cells in the myometrium.

Answer 63

Benign tumor (adenoma) of the thyroid. Note the normal-looking (well-differentiated), colloid-filled thyroid follicles.

Answer 64

Malignant tumor (adenocarcinoma) of the colon. Note that compared with the well-formed and normal-looking glands characteristic of a benign tumor (last card), the cancerous glands are irregular in shape and size and do not resemble the normal colonic glands. This tumor is considered differentiated because gland formation is seen. The malignant glands have invaded the muscular layer of the colon.

Answer 65

Well-differentiated squamous cell carcinoma of the skin. The tumor cells are strikingly similar to normal squamous epithelial cells, with intercellular bridges and nests of keratin pearls (arrow).

Answer 66

Anaplastic tumor showing cellular and nuclear variation in size and shape. The prominent cell in the center field has an abnormal tripolar spindle.

Answer 67

Pleomorphic tumor of the skeletal muscle (rhabdomyosarcoma). Note the marked cellular and nuclear pleomorphism, hyperchromatic nuclei, and tumor giant cells.

Answer 68

A, Carcinoma in situ. A low-power view shows that the epithelium is entirely replaced by atypical dysplastic cells. There is no orderly differentiation of squamous cells. The basement membrane is intact, and there is no tumor in the subepithelial stroma. B, A high-power view of another region shows failure of normal differentiation, marked nuclear and cellular pleomorphism, and numerous mitotic figures extending toward the surface.

Answer 69

**Differentiation refers to the extent to which neoplastic parenchymal cells resemble the corresponding normal parenchymal cells, both morphologically and functionally; lack of differentiation is called *anaplasia*.** In general, benign tumors are well differentiated. **While malignant neoplasms exhibit a wide range of parenchymal cell differentiation, most exhibit morphologic alterations that betray their malignant nature.** (Exceptions include well-differentiated SCCs and thyroid carcinomas) **Lack of differentiation, or anaplasia, is considered a hallmark of malignancy.**

Answer 70

Fibroadenoma of the breast. The tan-colored, encapsulated small tumor is sharply demarcated from the whiter breast tissue.

Answer 71

Microscopic view of fibroadenoma of the breast seen in last card. The fibrous capsule (right) delimits the tumor from the surrounding tissue.

Answer 72

Cut section of an invasive ductal carcinoma of the breast. The lesion is retracted, infiltrating the surrounding breast substance, and would be stony hard on palpation.

Answer 73

Low power microscopic view of invasive breast cancer. Note the irregular infiltrative borders without a well-defined capsule and intense stromal reaction.

Answer 74

Colon carcinoma invading pericolonic adipose tissue.

Answer 75

Axillary lymph node with metastatic breast carcinoma. Note the aggregates of tumor cells within the substance of the node and the dilated lymphatic channel.

Answer 76

A liver studded with metastatic cancer.

Answer 77

Microscopic view of lung metastasis. A colonic adenocarcinoma has formed a metastatic nodule in the lung.

Answer 78

Comparison between a benign tumor of the myometrium (leiomyoma) and a malignant tumor of the same origin (leiomyosarcoma).

Answer 79

**1. Pleomorphism** - variation in size and shape **2. Abnormal nuclear morphology** - Usually the nucleus is disproportionately large for the cell, causing high N:C ratio, shape is variable and often irregular, chromatin is coarsely clumped and distributed around the membrane or more darkly stained than normal (hyperchromatic) **3. Mitoses** - Many cells are in mitosis in poorly differentiated neoplasms, (high proliferative activity). The presence of mitoses does not necessarily indicate malignancy. However, very frequent, or atypical/bizzare mitotic figures are a more important feature. **4. Loss of polarity** - Orientation of cells is disturbed - sheets or large masses of tumor cells grow in an anarchic, disorganized fashion **5.** **Other changes** - Many malignant and some benign tumors may develop large central areas of ischemic necrosis due to insufficient vascular stroma.

Answer 80

Development of a cancer through stepwise acquisition of complementary mutations. The order in which various driver mutations occur in initiated precursor cells is not known and may vary from tumor to tumor.

Answer 81

* Metaplasia -* replacement of one type of cell with another type; nearly always found in association with tissue damage, repair, and regeneration (e.g. gastroesophageal reflux damages esophageal squamous epithelium --\> replacement by glandular (gastric/intestinal) epithelium more resistant to acid) * Dysplasia* - Disordered growth; usually in epithelial cells; loss in uniformity and architectural orientation (e.g. squamous cells losing the tall to flattened differentiation, and all appearing basilar) **When dysplastic changes are marked and involve the full thickness of the epithelium, but the lesion does not penetrate the basement membrane, it is considered a pre-neoplastic neoplasm, and is referred to as *carcinoma in situ*. Once tumors breach the BM, tumor is invasive. It does not always lead to cancer.** Often seen adjacent to invasive carcinoma, or in long-term cig smokers, it precedes cancer formation. It often occurs in metaplastic epithelium, but not all metaplastic epithelium is dysplastic.

Answer 82

Tumor evolution. Evolution of a renal cell carcinoma (left panel) and Darwin’s finches (right panel). The renal cell carcinoma evolutionary tree is based on genetic comparisons drawn from sequencing of DNA obtained from different tumor sites; the finch evolutionary tree was surmised by Darwin based on morphologic comparisons of different species of finches on the Galapagos Islands.

Answer 83

Hallmarks of cancer.

Answer 84

**The growth of cancers is accompanied by progressive infiltration, invasion, and destruction of the surrounding tissue, whereas nearly all benign tumors grow as cohesive, expansile masses that remain localized to their site of origin, and lack the capacity to infiltrate, invade, or metastasized to distant sites.** Benign tumors often contain a fibrous capsule, separating them from surrounding tissue, thus are easily excisable (exceptions - hemangiomas are unencapsulated). Malignant tumors are poorly demarcated from surrounding tissue **Next to the development of metastases, invasiveness is the most reliable feature that differentiates cancers from benign tumors.**

Answer 85

Growth factor signaling pathways in cancer. Growth factor receptors, RAS, PI3K, MYC, and D cyclins are oncoproteins that are activated by mutations in various cancers. GAPs apply brakes to RAS activation, and PTEN serves the same function for PI3K.

Answer 86

**Metastasis is defined by the spread of a tumor to sites that are physically discontinuous with the primary tumor, and unequivocally marks a tumor as malignant, as by definition, benign tumors do not metastasize.** All malignant tumors can metastasize; due to innate invasiveness, they can penetrate into blood vessels, lymphatics, and body cavities, through which they can spread. Some cancers metastasize very infrequently (e.g. gliomas, basal cell carcinomas of skin). Likelihood ofmetastasizing correlates with lack of differentiation, aggressive local invasion, rapid growth, and large size; WITH MANY EXCEPTIONS

Answer 87

**1.** **Seeding of body cavities and surfaces** - Occurs when neoplasm penetrates into open cavitary spaces (usually peritoneal, can be any); more common in epithelial neoplasms; coats body cavitary surfaces with heavy cancerous glaze; mucus-secreting appendiceal/ovarian carcinomas can fill cavity with a gelatinous neoplastic mass called *pseudomyxoma peritonei* * *2. Lymphatic spread** - **Transport through lymphatics is the most common pathway for the initial dissemination of carcinomas;** sarcomas may use this route too. * *A sentinel lymph node is defined as the first node in a regional lymphatic basin that receives lymph flow from the primary tumor, and can be biopsied to assess presence or absence of metastatic lesion.** **3. Hematogenous spread -** Typical of sarcomas, also seen with carcinomas. Veins have thinner walls and are more easily penetrated, but arterial involvement can happen at AV shunts or pulmonary capillary beds. Liver and lungs are most frequent first sites of hematogenous spread because of portal and pulmonary circulation.

Answer 88

The chromosomal translocation and associated oncogenes in Burkitt lymphoma and chronic myelogenous leukemia.

Answer 89

1. Environmental factors 2. Age 3. Acquired predisposing conditions 4. Genetic Predisposition

Answer 90

**Lthough both genetic and environmental factors contribute to the development of cancer, environmental influences appear to be the dominant risk factor for most cancers.** This is evidenced by the wide geographic variation in specific types of cancer. **Infectious agents**: 15% of all cancers worldwide caused by infectious agents (HPV - cervical carcinoma, EBV - lymphoma) **Smoking:** Cig smoking is the single most important environmental factor causing premature death in the US (larynx, mouth, pharynx, esophagus, pancreas, bladder, **lung** cancers) **Alcohol consumption Diet:**specifics unknown, but important factor **Obesity**: 52-62% higher incidence of cancer than normies **Reproductive history:** little is known **Environmental carcinogens**: UV rays, smog, arsenic in water, medications (methotrexate), asbestos

Answer 91

**Age has an important influence on the likelihood of being afflicted with cancer.** Most carcinomas occur later in life (\> 55 years) Cancer is the main cause of death in women 40-79, and men 60-79. Lower incidence after 80, because cancer patients do not live that long. Cancer accounts for \> 10% of deaths in children under 15yo in US. They get different types (small round blue cell tumors (neuroblastoma, Wilms tumor, retinoblastoma, acute leukemias, rhabdomyosarcoma)

Answer 92

**Acquired conditions that predispose to cancer can be divided into chronic inflammations, precursor lesions, and immunodeficiency states.** **1. Chronic inflammation**: usually carcinomas, but also mesothelioma and several types of lymphoma. Chronic inflammation leads to tissue repair and an increase in number of tissue stem cells., which are susceptible to neoplastic transformation. Immune cells involved in inflammation produce genotoxic ROS and inflammatory mediators that promote cell survival in the face of DNA damage. Chronic inflam leads to metaplasia, so cells are more able to survive ongoing insult. **2. Precursor lesions: localized morphologic changes associated with a high risk of cancer.** May arise in the setting of chronic inflammation and metaplasia (e.g. Barrett esophagus - gastric/colonic metaplasia in esophageal mucosa with gastric reflex; squamous metaplasia of bronchial mucosa with smoking). Others are noninflammatory hyperplasias (e.g. endometrial hyperplasia with sustained estrogen stimulation; leukoplakia: thickening of squamous epithelium in oral cavity, penis, vulva, may lead to SCC) Last group is benign neoplasms at risk for malignant transformation (colonic villous adenoma progresses to cancer in 50% of untreated cases) **3. Immunodeficiency states and cancer**: Immunodeficient patients, especially with T-cell deficits have increased risk for oncogenic virus-inducing cancers (lymphomas, certain carcinomas, rare sarcomas) **4. Genetic predisposition:** Some families have cancer as an inherited trait, usually due to mutations in tumor suppression gene. There is a complex interaction between genetic and nongenetic factors. Breast cancer has a strong hereditary component, but also is influenced by reproductive history.. Inherited variations (polymorphisms) of enzymes that metabolize procarcinogens to active carcinogenic forms can influence cancer susceptibility (cytochrome P-450 enzymes)

Answer 93

Pathogenesis of retinoblastoma. Two mutations of the RB locus on chromosome 13q14 lead to neoplastic proliferation of the retinal cells. In the sporadic form, both RB mutations in the tumor-founding retinal cell are acquired. In the familial form, all somatic cells inherit one mutated copy of RB gene from a carrier parent, and as a result only one additional RB mutation in a retinal cell is required for complete loss of RB function.

Answer 94

The role of RB in regulating the G1-S checkpoint of the cell cycle. Hypophosphorylated RB in complex with the E2F transcription factors binds to DNA, recruits chromatin-remodeling factors (histone deacetylases and histone methyltransferases), and inhibits transcription of genes whose products are required for the S phase of the cell cycle. When RB is phosphorylated by the cyclin D-CDK4, cyclin D-CDK6, and cyclin E-CDK2 complexes, it releases E2F. The latter then activates transcription of S-phase genes. The phosphorylation of RB is inhibited by cyclin-dependent kinase inhibitors, because they inactivate cyclin-CDK complexes. Virtually all cancer cells show dysregulation of the G1-S checkpoint as a result of mutation in one of four genes that regulate the phosphorylation of RB; these genes are RB, CDK4, the genes encoding cyclin D proteins, and CDKN2A (p16). TGF-β, transforming growth factor-β.

Answer 95

**1. Nonlethal genetic damage lies at the heart of carcinogenesis**. Initial damage may be environmental (viruses, chemicals, endogenous metabolites), inherited, or spontaneous and random **2. A tumor is formed by the clonal expansion of a single precursor cell that has incurred enetic damage (i.e. tumors are clonal).** All cells of the tumor have the same set of mutations present at the moment of transformation. Identified by DNA sequencing (point mutations) or chromosomal analyses (chromosomal translocations and copy number changes) * *3. Four classes of normal regulatory genes - the growth promoting proto-oncogenes, the growth-inhibiting tumor suppressor genes, genes that regulate programmed cell death (apoptosis), and genes involved in DNA repair** **- are the principal targets of cancer-causing mutations.** (1) Mutations in proto-oncogenes--\> "gain-of-function" --\> can transform cells when heterozygous (2) Mutations in tumor suppressor genes --\> "loss-of-function" --\> both alleles must be damaged for transformation. Exception: haploinsufficiency- reduces activity of protein enough to release brakes on cell proliferation/survival (3) Apoptosis-regulating gene mutations result in less death, enhanced survival; can be gain-of-function for genes whose products suppress apoptosis or loss-of-function for genes whose products promote apoptosis (4) Mutations in DNA repair genes: Loss-of-function mutations impair cell ability to recognize and repair nonlethal genetic damage --\> affected cells acquire mutations at an accelerated rate (*mutator phenotype*, marked by *genomic instability*) **4. Carcinogenesis results from the accumulation of complementary mutations in a stepwise fashion over time. Malignant neoplasms have several phenotypic alterations known as *cancer hallmarks* (excessive growth, local invasiveness, distant mets)** **5. Mutations that contribute to teh development of the malignant phenotype are referred to as *driver mutations*.** The *initiating mutation* is teh first driver starting a cell on the path to malignancy, and is present in all cells of the cancer. "Initiated" cell acquires numerous further driver mutations, which all contribute to development of cancer. **6. Loss-of-function mutations in genesthat maintain genomic integrity appear to be a common early step on teh road to malignancy, particularly in solid tumors.** These mutations lead to increased likelihood of acquiring driver mutations, and increased frequency of mutations that have no phenotypic consequence, *passenger mutations*.

Answer 96

The role of p53 in maintaining the integrity of the genome. Activation of normal p53 by DNA-damaging agents or by hypoxia leads to cell cycle arrest in G1 and induction of DNA repair by transcriptional upregulation of the cyclin-dependent kinase inhibitor CDKN1A (encoding the cyclin-dependent kinase inhibitor p21) and the GADD45 genes. Successful repair of DNA allows cells to proceed with the cell cycle; if DNA repair fails, p53 triggers either apoptosis or senescence. In cells with loss or mutations of the p53 gene, DNA damage does not induce cell cycle arrest or DNA repair, and genetically damaged cells proliferate, giving rise eventually to malignant neoplasms.

Answer 97

The role of APC in regulating the stability and function of β-catenin. APC and β-catenin are components of the WNT signaling pathway. A, In resting colonic epithelial cells (not exposed to WNT), β-catenin forms a macromolecular complex containing the APC protein. This complex leads to the destruction of β-catenin, and intracellular levels of β-catenin are low. B, When normal colonic epithelial cells are stimulated by WNT molecules, the destruction complex is deactivated, β-catenin degradation does not occur, and cytoplasmic levels increase. β-catenin translocates to the nucleus, where it binds to TCF, a transcription factor that activates genes involved in cell cycle progression. C, When APC is mutated or absent, as frequently occurs in colonic polyps and cancers, the destruction of β-catenin cannot occur. β-catenin translocates to the nucleus and coactivates genes that promote entry into the cell cycle, and cells behave as if they are under constant stimulation by the WNT pathway.

Answer 98

Metabolism and cell growth. Quiescent cells rely mainly on the Krebs cycle for ATP production; if starved, autophagy (self-eating) is induced to provide a source of fuel. When stimulated by growth factors, normal cells markedly upregulate glucose and glutamine uptake, which provide carbon sources for synthesis of nucleotides, proteins, and lipids. In cancers, oncogenic mutations involving growth factor signaling pathways and other key factors such as MYC deregulate these metabolic pathways, an alteration known as the Warburg effect.

Answer 99

By the time tumors come to clinical attention (usually 1 gram, 10⁹ cells), has undergone a minimum of 30 cell doublings (likely a substantial underestimation). Tumors become more aggressive over time (i.e. *tumor progression*). **Selection of the fittest can explain not only the natural history of cancer, but also changes in tumor behavior following therapy.** **In addition to DNA mutations, epigenetic aberrations also contribute to malignant properties:** DNA methylation silences gene expression, histone modification can enhance or dampen gene expression

Answer 100

Intrinsic and extrinsic pathways of apoptosis and mechanisms used by tumor cells to evade cell death. (1) Loss of p53, leading to reduced function of pro-apoptotic factors such as BAX. (2) Reduced egress of cytochrome c from mitochondria as a result of upregulation of anti-apoptotic factors such as BCL2, BCL-XL, and MCL-1. (3) Loss of apoptotic peptidase activating factor 1 (APAF1). (4) Upregulation of inhibitors of apoptosis (IAP). (5) Reduced CD95 level. (6) Inactivation of death-induced signaling complex. FADD, Fas-associated via death domain.

Answer 101

Escape of cells from senescence and mitotic catastrophe caused by telomere shortening. Replication of somatic cells, which do not express telomerase, leads to shortened telomeres. In the presence of competent checkpoints, cells undergo arrest and enter nonreplicative senescence. In the absence of checkpoints, DNA repair pathways, such as the nonhomologous end-joining (NHEJ) pathway are inappropriately activated, leading to the formation of dicentric chromosomes. At mitosis the dicentric chromosomes are pulled apart, generating random double-stranded breaks, which then activate DNA-repair pathways, leading to the random association of double-stranded ends and the formation, again, of dicentric chromosomes. Cells undergo numerous rounds of this bridge-fusion-breakage cycle, which generates massive chromosomal instability and numerous mutations. If cells fail to reexpress telomerase, they eventually undergo mitotic catastrophe and death. Reexpression of telomerase allows the cells to escape the bridge-fusion-breakage cycle, thus promoting their survival and tumorigenesis.

Answer 102

Origins of cells with self-renewing capacity in cancer. Cancer stem cells can arise from transformed tissue stem cells (e.g., hematopoietic stem cells in chronic myelogenous leukemia, CML) with intrinsic “stemness” or from proliferating cells that acquire a mutation that confers “stemness” (e.g., granulocyte progenitors in acute promyelocytic leukemia). In both instances, the cancer stem cells undergo asymmetric cell divisions that give rise to committed progenitors that proliferate more rapidly than the cancer stem cells; as a result, most of the malignant cells in both tumors lack self-renewing capacity.

Answer 103

**1. Self-sufficiency in growth signals -** usually due to oncogene activation **2. Insensitivity to growth-inhibitory signals -** Usually because of inactivation of tumor suppressor genes **3. Altered cellular metabolism -** (i.e. Warburg effect: tumor cells switch to aerobic glycolysis, enabling macromolecule and organelle synthesis **4. Evasion of apoptosis** **5. Limitless replicative potential (immortality) -** helps tumor cells avoid cellular senescence and mitotic catastrophe **6. Sustained angiogenesis** **7. Ability to invade and metastasize -** Due to intrinsic properties of tumor cells and signals initiated by tissue response **8. Ability to evade the host immune response**

Answer 104

The metastatic cascade. Sequential steps involved in the hematogenous spread of a tumor.

Answer 105

Sequence of events in the invasion of epithelial basement membranes by tumor cells. Tumor cells detach from each other because of reduced adhesiveness and attract inflammatory cells. Proteases secreted from tumor cells and inflammatory cells degrade the basement membrane. Binding of tumor cells to proteolytically generated binding sites and tumor cell migration follow.

Answer 106

**1. Genomic instability** **2. Tumor-associated inflammation** These enable cellular transformation and tumor progression

Answer 107

**1. Oncogene: gene that promotes autonomous cell growth in cancer cells** **2. Proto-oncogene: unmutated cellular counterparts of oncogenes** **3. Oncoprotein: Mutated protein resembling the normal products of proto-oncogenes, whose activity does not depend on external signals** **Oncogenes are created by mutations in proto-oncogenes and encode oncoproteins that have the ability to promote cell growth in the absence of normal growth-promoting signals**

Answer 108

1. Binding of a growth factor to its receptor 2. Transient and limited activation of growth factor receptor, which activates several cytoplasmic signal-tranducing proteins 3. Transmission of the transduced signal to the nucleus via additional cytoplasmic effector proteins and second messengers or by a cascade of signal transduction molecules 4. Induction and activation of nuclear regulatory factors that initiate DNA transcription 5. Expression of factors that promote entry and progression of the cell into the cell cycle, ultimately resulting in cell division 6. Parallel changes in other genes that support cell survival and metabolic alterations needed for optimal growth

Answer 109

1. Tyrosine kinase pathway 2. G protein-coupled pathway 3. JAK/STAT pathway 4. WNt pathway 5. Notch pathway 6. Hedgehog pathway 7. TGF-b/SMAD pathway 8. NF-kB pathway **Tyrosine kinase pathways are the most frequently mutated in human neoplasms**

Answer 110

**As a result of this constitutive activity, pro-growth oncoproteins endow cells with self-sufficiency in growth**

Answer 111

Autocrine loop: some cancer cells can synthesize the same growth factors to which they're responsive (i.e. glioblastomas express PDGF and PDGF receptor tyrosine kinases)

Answer 112

**1. ERBB1:** encodes epidermal growth factor receptor (EGFR) which get point mutations related to cancers (i.e. lung adenocarcinoma). These mutations result in constitutive EGFR tyrosine kinase activation **2. ERBB2:** encodes HER2 which is amplified, rather than point mutated, in breast carcinoma. Leads to overexpression of HER2 receptor and constitutive TK activation **3. Gene rearrangements**: Activate other receptor tyrosine kinases (i.e. ALK). A deletion in chromosome 5 fuses ALK gene with EML4 gene in lung adenocarcinomas

Answer 113

RAS MAPK cascade and PI3K / AKT pathway

Answer 114

**Point mutations of the RAS family** These are present in 15-20% of all human tumors. Expressed in much higher rates in specific tumors 90% of pancreatic adenocarcinomas and cholangiocarcinomas 50% of colon, endometrial, thyroid cancer 30% of lung adenocarcinomas, myeloid leukemias

Answer 115

1. Part of a family of membrane-associated small G proteins that bind GTP, GDP 2. They normally flip back and forth between excited signal-transmitting state (bound to GTP) and a quiescent state (bound to GDP) 3. When GFs stimulate TK receptor, GTP binds and activates RAS, which stimulates MAPK and PI3K/AKT pathways 4. These result in phosphorylation and activation of numerous molecules promoting rapid cell growth 5. RAS activation is transient due to intrinsic GTPase activity, accelerated by GTPase-activating proteins (GAPs) **Several distinct RAS point mutations have been found that markedly reduce GAP activity**

Answer 116

* *Mutations in BRAF** 1. Detected in close to 100% of hairy cell leukemias, \> 60% of melanomas, 80% of benign nevi 2. BRAF is a serine/threonine protein kinase that sits at the top of a cascade of other serine/threonine kinases of the MAPK family 3. Activating mutations in BRAF stimulate downstream kinases and activate transcription factors * *Mutations in PI3K family** 1. Very common in certain cancers 2. Normally, like BRAF, PI3K activates a cascade of serine/threonine kinases (i.e. AKT) (a. ) AKT has many substrates i. mTOR - a sensor of cellular nutrient status, is activated by AKT to stimulate protein and lipid synthesis ii. BAD - a pro-apoptotic protein that is inactivated by AKT, enhancing cell survival iii. FOXO transcription factors - promote apoptosis, and are negatively regulated by AKT 3. PI3K is negatively regulated by an important "braking factor" - PTEN 4. All factors mentioned can be mutated to contribute to cancer, but **PI3K and PTEN** are most frequently mutated.

Answer 117

1. These often occur as chromosomal translocations or rearrangements that create fusion genes encoding constitutively active tyrosine kinases (e. g. ABL tyrosine kinase translocation and fusion with BCR gene resulting in constitutively active, oncogene BCR-ABL tyrosine kinase) This mechanisminvolved in CML and some ALLs, and specific, low toxicity treatment has been very successful, a good example of *oncogene addiction-* tumor cells are highly dependent on activity of one or more oncogenes. 2. Nonreceptor TKs can be activated by point mutations that decrease inhibitory domains (e.g. JAK/STAT pathway induces mitogenesis. Point mutation in JAK2 are highly associated with essential thrombocytosis, polycythemia vera, primary myelofibrosis

Answer 118

The ultimate consequence of deregulated mitogenic signaling pathways is inappropriate and continuous stimulation of nuclear transcription factors that drive growth-promoting genes. Transcription factor mutations in TFs that regulate pro-growth genes and cyclin expression can lead to growth autonomy and cancer Examples: **MYC,** MYB, JUN, FOS, REL

Answer 119

1. MYC proto-oncogene expressed in all cells, and is an immediate/early response gene, which is rapidly and transiently induced by RAS/MAPK signaling following GF stimulation 2. MYC protein concentrations are tightly controlled at transcription, ,translation, stability levels, and all pathways that regulate growth impinge on MYC. 3. MYC has very broad activities, including: (1) **MYC activates the expression of many genes that are involved in cell growth** i. Some MYC target D cyclin genes, involved in cell cycle progression ii. MYC upregulates rRNA gene expression and rRNA processing, enhancing capability for protein synthesis iii. MYC upregulates genes (glycolytic enzymes, glutamine metabolism enzymes) , resulting in Warburg effect (2) **MYC upregulates expression of telomerase** (3) **MYC is one of a handful of TFs that can act together to reprogram somatic cells into pluripotent cells** 3. MYC can be deregulated in a variety of ways (1) Genetic alterations in MYC gene (e.g. MYC translocations in Burkitt lymphoma, MYC amplification in breast, colon, ung carcinomas) (2) Oncogenic mutations in upstream signaling pathways can lead to elevated MYC protein levels (e.g. constitutive RAS/MAPK signaling (many cancers), Notch signaling (several hematologic cancers), Hedgehog signaling (medulloblastoma), and Wnt signaling (colon carcinoma))

Answer 120

1. Progression of cells through the cell cycle is orchestrated by CDKs, which are activated by binding to cyclins. CDKIs (inhibitors) exert negative control over the cell cycle 2. **There are two main cell cycle checkpoints; one at the G1/S transition and one at the G2/M transition, each of which is tightly regulated by a balance of growth promoting and growth suppressing factors, as well as sensors of DNA damage.** (1) Defects in the G1/S checkpoint are most important in cancer, as they lead to dysregulated growth and a mutator phenotype. The major cancer-associated mutations affecting the G1/S checkpoint are in two broad classes: a. **Gain-of-function mutations in D cyclin genes and CDK4, oncogenes that promote G1/S progression** (Cyclins D1, D2, D3 can get translocation or amplification mutations. CDK4 amplification occurs in several cancers. b. **Loss-of-function mutations in tumor suppressor genes that inhibit G1/S progression** (CDKIs frequently mutated (e.g. p16 mutations in melanoma-prone people; acquired p16 inactivation in pancreatic carcinomas, glioblastomas, others)

Answer 121

**growth inhibition**

Answer 122

- Two mutations (hits), involving both alleles of RB at chromosome locus 13q14, are required to produce retinoblastoma - In familial cases, children inherit one defective RB copy and one normal copy. Retinoblastoma develops when the normal RB allele is mutated in retinoblasts due to a spontaneous somatic mutation; this is virtually inevitable - In sporadic cases, both normal RB alleles must undergo somatic mutation in the same retinoblast - very low probability In general, familial cancers involving any tumor suppressor gene mutations follow this pattern; risk of cancer is inherited in autosomal dominant fashion, and tumors require a second hit in the normal allele for cancer to manifest.

Answer 123

RB and p53 They cause quiescence or permanent cell cycle arrest (oncogene-induced senescence)

Answer 124

**RB, a key negative regulator of the G1/S cell cycle transition, is directly or indirectly inactivated in most human cancers.** RB controls cell differentiation; it is active and hypophosphorylated in quiescent cells, and inactive and hyperphosphorylated in cells passing through G1/S transition. Two ways RB function may be compromised: (1) Loss-of-function mutations involving both RB alleles (2) Shift from active to inactive state by gain-of-function mutations that upregulate CDK/cyclin D, E activity (CDK4/D, CDK6/D, CDK2/E) OR loss-of-function mutations that inhibit CDK inhibitors **Loss of normal cell cycle control is central to malignant transformation and at least one of four key regulators of the cell cycle (p16/INK4a, cyclin D, CDK4, RB) is dysregulated in the vast majority of cancers.**

Answer 125

**TP53, a tumor suppressor gene that regulates cell cycle progression, DNA repair, cellular senescence, and apoptosis, is the most frequently mutated gene in human cancers.** Like RB, many tumors without TP53 mutations have other mutations affecting proteins that regulate p53 function (e.g. MDM2 amplifications, which normally degrades p53 protein) p53 protein is undetectable in normal cells. In stressed cells, p53 is released from inhibitory effects of MDM2 via 2 mechanisms: (1) *DNA damage and hypoxia*: ataxia-telangiectasia mutated (ATM) and ataxia-telangiectasia and Rad3 related (ATR) proteins are initiators of p53 activation (2) *Oncogenic stress*: Oncoprotein activation (e.g. RAS) leads to sustained signalign through MAPK and PI3K/AKT pathways --\> increased expression of p14/ARF, which binds MDM2 and displaces p53 * *Once activated, p53 thwarts neoplastic transformation by inducing transient cell cycle arrest, permanent senescence, or apoptosis**. (1) **Transient p53-induced cell cycle arrest:** Occurs late in G1 phase, caused by p53-dependent transcription of CDKN1A gene, which encodes CDKI p21, which inhibits CDK4/D cyclin, keeping RB activated. p53 also induces GADD45 to enhance DNA repair (2) **p53-induced senescence:** Permanent cell cycle arrest, may be due to epigenetic changes causing heterochromatin at key loci. (3) **p53-induced apoptosis**: ultimate protective mechanism against neoplastic transformation. p53 directs BAX and PUMA (pro-apoptotic genes) **With loss of p53 function, DNA damage goes unrepaired, driver mutations accumulate in oncogenes, and the cell marches blindly along a dangerous path leading to malignant transformation.**

Answer 126

**Even in the presence of ample oxygen, cancer cells demonstrate a distinctive form of cellular metabolism characterized by high levels of glucose uptake and increased conversion of glucose to lactose (fermentation) via the glycolytic pathway (i.e. the Warburg effect)**. **Aerobic glycolysis provides rapidly dividing tumor cells with metabolic intermediates that are needed for synthesis of cellular components, whereas mitochondrial oxidative phosphorylation does not.** * *Metabolic reprogramming is produced by signaling cascades downstream of growth factor receptors, the same pathways that are deregulated by mutations in oncogenes and tumor suppressor genes:** (1) **PI3K/AKT signaling**: upregulates glucose transporters and glycolytic enzymes, promotes shunting of mitochondrial intermediates leading to lipid synthesis, and stimulates protein synthesis (2) **Receptor tyrosine kinase activity**: phosphorylate pyruvate kinase, inhibiting it, and leading to a build up of glycolytic intermediates (3) **MYC:** upregulated by pro-growth pathways, MYC transcription factor supports anabolic metabolism and cell growth by upregulating glycolytic enzymes and glutaminase ***Autophagy:*** may help or hurt tumor cells

Answer 127

**Accumulation of neoplastic cells may result not only from activation of growth-promoting oncogenes or inactivation of growth-suppressing tumor suppressor genes, but also from mutations in the genes that regulate apoptosis.** **The intrinsic (mitochondrial) pathway of apoptosis is most frequently disabled in cancer.**

Answer 128

**All cancers contain cells that are immortal and have limitless replicative potential due to three critical factors:** **1. Evasion of senescence:** Senescence is associated with upregulation of p53 and Ink4a/p16 which maintain RB in a hypophosphorylated state, promoting cell cycle arrest. RB-dependent G1/S checkpoint disrupted in all cancers. **2. Evasion of mitotic crisis:** Mitotic crisis is attributed to shortening of telomeres. If cells in this crisis reactivate telomerase, they can restore telomeres and survive. **3. Self-renewal:** Each time a stem cell divides, at least one of the two daughter cells remains a stem cell. (in symmetric division, both daughters are stem cells).

Answer 129

**Even if a solid tumor possesses all of the genetic aberrations that are required for malignant transformation, it cannot enlarge beyond 1-2 mm diameter unless it can induce angiogenesis.** Most tumors cannot induce angiogenesis early on, and remain small or in situ until an *angiogenic switch* occurs. Balance of angiogenic / anti-angiogenic factors influenced by: (1) Lack of O2 stabilizes HIF1a, which activates VEGF and bFGF (2) Mutations in tumor suppressors and oncogenes promote angiogenesis (e.g. p53 can stimulate antiangiogenic molecules, thrombospondin-1, and repress VEGF) (3) Transcription of VEGF influenced by RAS-MAP kinase signals and gain-of-function mutations in RAS or MYC

Answer 130

**Invasion and metastasis are the results of complex interactions between cancer cells and normal stroma and are the major causes of cancer-related morbidity and mortality.** Metastatic cascade is divided into two phases: 1. *Invasion of extracellular matrix*: (1) Loosening up of tumor cell-tumor cell interactions: **Dissociation of cancer cells from one another is often the result of alterations in intercellular adhesion molecules and is the first step in the process of invasion.** Loss of E-cadherin function may mediate this process. (2) Degradation of ECM: **Degradation of basement membrane and interstitial connective tissue is the second step of invasion.** This is done by elaboration of proteolytic enzymes (MMPs, cathepsin D, urokinase plasminogen activator) (3) Attachment to novel ECM components (4) Migration and invasion of tumor cells: **Locomotion is the final step of invasion, propelling tumor cells through the degraded basement membranes and zones of matrix proteolysis.** *2. Vascular dissemination and homing of tumor cells*: Tumor cells aggregate in clumps within circulation due to homotypic adhesion and heterotypic adhesion with blood cells, mainly platelets.CD44 adhesion molecule expressed on normal T lymphs helps tumor clumps migrate to lymphoid tissue (solid tumors often express CD44). **The site at which circulating tumor cells leave the capillaries to form secondary deposits is related to the anatomic location and vascular drainage of the primary tumor and tropism of particular tumors for specific tissues.** Tropism related to the following: (1) Adhesion molecules with specific ligands in organs (2) Chemokines (e.g. breast cancer cells expressing chemokine receptors CXCR4, CCR7) (3) target tissue may be a nonpermissive environment

Answer 131

Several competing theories proposed to explain how metastatic phenotype arises: 1. *clonal evolution model*: As mutations accumulate in genetically unstable cancer cells, a rare subset of subclones acquires a pattern of gene expression that is permissive for metastasis steps 2. Subset of breast cancers may have a '*metastasis signature'*, a gene expression causing prediliction for metastasis 3. Metastatic signature may be necessary but also additional mutations (above two combined) 4. Capacity for metastasis may involve characterstics of microenvironment such as stromal components and angiogenesis Possible metastasis oncogenes: SNAIL, TWIST - encode transcription factors that promote epithelial-to-mesenchymal transition (EMT)

Chapter 7: Neoplasia Flashcards

(184 cards)