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Year 1 POM > Cancer Genetics > Flashcards

Cancer Genetics Flashcards

1
Q

What is cancer?

A
  • All cancers derive from single cells that have acquired the characteristics of continually dividing in an unrestrained manner and invading surrounding tissues.
  • Cancer cells behave in this abnormal manner because of changes in the DNA sequence of key genes, which are known as cancer genes. Therefore all cancers are genetic diseases.
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2
Q

What is a benign tumour?

A

•A benign tumor is a mass of well-differentiated cells that grows slowly, is capsulated and lacks the ability to invade neighboring tissue or metastasize

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3
Q

What is a malignant tumour?

A

•A malignant tumor is not self-limited in its growth (escapes apoptosis, is able to produce new blood vessels), cells are poorly differentiated and capable of invading into adjacent tissues, and may be capable of spreading to distant tissues (metastasis)

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4
Q

How can cancer begin?

A

-Multi step carcinogenesis
•Cancer may begin because of the accumulation of mutations involving oncogenes, tumor suppressor genes, and DNA repair genes.

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5
Q

What is an example of multi step carcinogenesis?

A

-Colon cancer can begin with a defect in a tumor suppressor gene (APC) that allows excessive cell proliferation.
-The proliferating cells then tend to acquire additional mutations involving DNA repair genes, other tumor suppressor genes (p53), and many other growth-related genes (K-ras).
•Over time, the accumulated damage can yield a highly malignant, metastatic tumor.

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6
Q

What is the microscopic appearance of cancer cells?

A

e

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7
Q

What are carcinomas?

A
  • the most common types of cancer arise from the cells that cover external and internal body surfaces.
  • Lung, breast, and colon are the most frequent cancers of this type (epithelial)
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8
Q

What are sarcomas?

A

are cancers arising from cells found in the supporting tissues of the body such as bone, cartilage, fat, connective tissue and muscle

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9
Q

What are lymphomas?

A

are cancers that arise in the lymph nodes and tissues of the body’s immune system
are cancers of the immature blood cells that grow in the bone marrow and tend to accumulate in large numbers in the bloodstream

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10
Q

What causes cancers?

A
  • Chemicals (e.g. from smoking) and radiation can damage genes (environment)
  • Viruses can introduce their own genes into cells (exogenous factors)
  • By heredity, alterations in genes that make a person more susceptible to cancer can be passed to the next generation (genetics – rare and common)

Genes are altered, or “mutated,” in various ways as
part of the mechanism by which cancer arises.
All lead to abnormal cellular regulation

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11
Q

What are leukaemia’s?

A

are cancers of the immature blood cells that grow in the bone marrow and tend to accumulate in large numbers in the bloodstream

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12
Q

What are the hallmarks of cancer?

A
  1. Deregulating cellular energetics
  2. Avoid immune destruction
  3. Genome instability
  4. Tumour-promoting inflammation
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13
Q

How do tumours evade the immune response?

A
  1. Tumour cells release tumour antigens
  2. Antigen-presenting cells gather tumour antigens and activate T cells
  3. Activated T cells target and eliminate cancer cells throughout the body
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14
Q

What are germline mutations?

A
  • A gene change in a body’s reproductive cell (egg or sperm) that becomes incorporated into the DNA of every cell in the body of the offspring either before or during meiosis
  • Germline mutations are passed on from parents to offspring. Also called a hereditary mutation
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15
Q

What are somatic mutations?

A
  • Occur during mitosis anywhere in the body except reproductive cells (egg or sperm), also known as acquired or sporadic mutations.
  • Will not be passed on
  • These alterations can (but do not always) cause cancer or other diseases.
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16
Q

What are the different types of mutation?

A
  • Deletions
  • Duplications
  • Inversions
  • Translocations
  • Single base substitutions (point mutations – silent, nonsense, missense)
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17
Q

What are the other types of genetic mutation?

A
  • Chromosome instability

- Aneuploidy

18
Q

What are some distinct somatic mutations in cancer?

A

G>T

C>T

19
Q

What does the DNA damage from UV radiation lead to?

A

formation of covalent bonds between two adjacent pyridimines (C and T) in the
DNA molecule

20
Q

What are passenger mutations?

A

many mutations can be tolerated by somatic cells (often in heterozygote state)

21
Q

What are driver mutations?

A

few mutations can confer a selective advantage and are recurrently found (in homozygote state)

22
Q

What is the lifetime risk of developing cancer in a particular tissue correlated to?

A

The life time risk of developing cancer in a particular tissue is correlated (r=o.8)
with how often stem cells in that tissue divide

23
Q

What are oncogenes?

A

One mutation is sufficient for role in cancer development

DOMINANT, GAIN OF FUNCTION

24
Q

What are acquired mutations in oncogenes?

A
  • Most cancer-causing mutations involving oncogenes are acquired, not inherited.
  • They generally activate oncogenes by chromosome rearrangements, gene duplication, or mutation.
  • For example, a chromosome rearrangement can lead to formation of the gene called BCR-ABL -> leads to chronic myeloid leukemia (CML).
25
Q

What are inherited mutations in oncogenes?

A

•A few cancer syndromes are caused by inherited mutations of proto-oncogenes that cause oncogene to be turned on or activated

26
Q

What are some examples of inherited mutations in oncogenes?

A
  • Multiple Endocrine Neoplasia Type 2 (MEN2) is caused by an inherited mutation in the gene called RET à people affected by this syndrome often develop an uncommon thyroid cancer called medullary cancer of thyroid
  • Inherited mutations in the gene called KIT - hereditary gastrointestinal stromal tumors (GISTs).
  • Inherited mutations in the gene called MET - hereditary papillary renal cancer
  • Inherited mutations in the gene called CDK4 - Malignant melanoma
27
Q

What is two-hit hypothesise?

A
  • In 1971, Dr. Alfred Knudson proposed the two-hit hypothesis to explain the early onset at multiple sites in the body of an inherited form of cancer called hereditary retinoblastoma
  • Most loss-of-function mutations that occur in tumor suppressor genes are recessive in nature, thus in order for a particular cell to become cancerous, both of the cell’s tumor suppressor genes must be mutated.
  • In the first event in the two-hit model is an inherited mutation, however inheriting one germline copy of a damaged gene present in every cell in the body is not sufficient to enable this cancer to develop.
  • A second hit (or loss) to the good copy in the gene pair could occur somatically, producing cancer.
  • This hypothesis predicts that the chances for a germline mutation carrier to get a second somatic mutation at any of multiple sites in his/her body cells is much greater than the chances for a non-carrier to get two hits in the same cell.
28
Q

What is p53?

A

•p53 is also known as protein 53 or tumor protein 53, is a tumor suppressor protein that in humans is encoded by the TP53 gene

29
Q

Why is it important to regulate the cell cycle?

A

•It is important to regulate the cell cycle and it functions as a tumor suppressor gene to prevent cancer. If the TP53 gene is damaged, tumor suppression function is severely reduced.

30
Q

What happens to people who inherit only one functional copy of the TP53 gene?

A

most likely develop tumors in early adulthood, a disorder known as Li-Fraumeni syndrome.

31
Q

How can the TP53 gene also be damaged in cells?

A

by mutagens (chemicals, radiation, or viruses), increasing the likelihood that the cell will begin decontrolled division.

32
Q

What happens in a loss of TP53 gene (due to mutations or deletion)?

A

occurs in >50% of human cancers (almost100% of high grade serous ovarian cancers)

33
Q

What are these cancer cells genetically unstable?

A

-Unable to do:
-Stop the cell cycling to allow time for DNA repair
-Carry out efficient DNA repair
-Undergo apoptosis

34
Q

What are DNA repair genes?

A

code for proteins whose normal function is to correct errors that arise when cells duplicate their DNA prior to cell division.

35
Q

What is the rate of DNA repair dependent on?

A

many factors, including the cell type, the age of the cell, and the extracellular environment.

36
Q

What are the three possible stats for a cell that has accumulated a large amount of DNA damage, or one that no longer effectively repairs damage incurred to its DNA?

A

-an irreversible state of dormancy
-cell suicide, also known as apoptosis or programmed cell death
-unregulated cell division, which can lead to the formation of a tumor that is cancerous

37
Q

What can mutations in DNA repair genes lead to?

A

a failure in repair, which in turn allows subsequent mutations to accumulate.

38
Q

What is BRCA1 in DNA repair?

A

BRCA1 is phosphorylated by ATM and CHK2 in response to double – stranded DNA breaks (i.e. these could be produced due for example by ionizing radiation).

39
Q

How are BRCA1 and BRCA2 used in DNA repair?

A

BRCA1 binds to BRCA2 which interacts with RAD51 to form a complex which is involved in DNA repair

40
Q

How is bacteria involved in stomach cancer?

A
  • The bacterium Helicobacter pylori, which can cause stomach ulcers, has been associated with the development of cancer, so people infected with H. pylori are at increased risk for stomach cancer.
  • 50% of pop. infected, incidence of stomach cancer 1 in 64 (men), 1 in 120 (women)
  • Research is under way to define the genetic interactions between this infectious agent and its host tissues that may explain why cancer develops.
41
Q

What is cancer caused by?

A
  • Cancer as a common disease with multifactorial inheritance, involving both genetic and environmental factors (Exposure to mutagens, such as X-rays, UV radiation, mutagens in tobacco smoke, food intake)
  • Most cases of cancer, perhaps 80 to 90 percent, occur in people with no family history of the disease.
42
Q

How do we identify cancer susceptibility genes?

A
  • Studying the genetic predisposition to developing cancer has been a vast and productive undertaking since early linkage studies of high-risk families identified rare and highly penetrant loci (those with large effect size) such as BRCA1 and BRCA2 for breast cancer and adenomatous polyposis coli (APC) gene for colorectal cancer
  • In recent years genome wide association studies have led to the discovery of many common low risk variants for different cancers.

Year 1 POM (39 decks)

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