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Role of genetic changes in carcinogenesis Flashcards

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1
Q

What is carcinogenesis?

A

Process of how a normal cell evolves into an invasive cancer cell

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2
Q

How much of carcinogenesis is a genetic process?

A

It is mostly a genetic process

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3
Q

Why is carcinogenesis mostly a genetic process?

A

It results from accumulation of multiple genetic changes

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4
Q

What 2 types of genes undergo genetic changes in carcinogenesis?

A

Oncogenes

Tumour suppressor genes

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5
Q

In the normal cell phenotype, how can cell regulation be described?

A

Highly regulated cell growth and division

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6
Q

What 2 kinds of signals control different stages of the cell-cycle in a normal cell phenotype?

A

Intracellular and extracellular signals

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7
Q

In the normal cell phenotype, how can an extracellular signal from a cell produce a response in another cell?

A

The extracellular signal molecule binds to the complementary receptor on the other cell, producing a response in the other cell

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8
Q

In the normal cell phenotype, does every cell type has the same set of receptors?

A

No, each cell type has a characteristic set of receptors

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9
Q

How do signalling molecules interact in the normal cell phenotype to regulate the cell?

A

Different combinations of extracellular signalling molecules needed to regulate division, differentiation, survival

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10
Q

If appropriate extracellular signals are missing, how does the normal cell phenotype typically respond?

A

Undergoes apoptosis

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11
Q

How is cell growth regulated in the cancer cell phenotype compared to the normal cell phenotype?

A

In cancer cell phenotype there is loss of control of cell growth, but in the normal cell phenotype cell growth is highly regulated

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12
Q

What are the 3 main cancer hallmarks that cause a normal cell to become tumourigenic?

A

Cell immortalisation

Cell fails to follow normal growth constraints

Cell invasion of normal tissues

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13
Q

How does cell immortalisation develop in the cancer cell phenotype?

A

Cell undergoes indefinite growth

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14
Q

How does cancer cell phenotype evade normal growth constraints?

A

Becomes independent of growth factors

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15
Q

How does cancer cell phenotype invade normal tissues?

A

The cancer cell invades basement membrane of origin tissue and spreads to other organs to establish colonies in

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16
Q

What is the name of the process of cancer cell invasion of normal tissues in other organs?

A

Metastasis

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17
Q

What 3 factors occur in carcinogenesis that make it a micro-evolutionary process?

A

Genetic change

Competition between aggressive clones

Natural selection

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18
Q

What is the effect of heritable changes in a cancer cell?

A

Changes function of cell operation

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19
Q

Give 3 examples of functional changes that occur in cellular operation due to heritable changes?

A

Protein underexpressed or overexpressed

Protein changes function

Regulatory pathway changed

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20
Q

What are the 3 main heritable changes that occur in a cancer cell?

A

Dominant driver mutation of oncogenes

Recessive driver mutation of tumour suppressor genes

Epigenetic changes

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21
Q

When dominant driver mutation of an oncogene occurs, how many alleles of the oncogene need to mutate to express the phenotype?

A

One allele of the oncogene, as it is a dominant mutation

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22
Q

What is the effect of the dominant driver mutation of oncogenes?

A

Oncogene products have been altered so have different function

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23
Q

What is the effect of recessive drive mutation of both tumour suppressor genes in the cancer cell phenotype?

A

Tumour suppressor genes undergo loss of function

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24
Q

Does epigenetic change alter the gene sequence of cancer cells?

A

No, it modifies the sequence eg. methylation

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25
What is a driver mutation?
Alteration that gives cancer cell a survival advantage for its neoplastic transformation
26
What is a passenger mutation?
Alteration that has no effect on cancer cell fitness but is detected in cells that also have a driver mutation
27
How do passenger mutations demonstrate the hitch-hiker effect?
When cancer cells undergo clonal expansion, passenger mutations are also replicated
28
What are the 4 types of DNA mutations?
Substitution, deletion, insertion, copy number changes
29
How does DNA substitution occur?
A base in the genome is exchanged for another base
30
How does DNA deletion occur?
One base/multiple bases are removed from genome
31
How does DNA insertion occur?
One base/multiple bases are added to genome
32
How do DNA copy number changes occur?
Large section of genome is deleted, duplicated or has many copies
33
How do translations/chromosomal rearrangements occur?
Genome is cut in 2 places and joined, which can also lead to gene fusions
34
How do genetic changes cause different functional proteins to be synthesised?
Transcribed mRNA sequence is different, so codons will be complementary to different amino acids, so a different amino acid sequence is formed in translation
35
What 3 factors cause genetic change to occur in a cell's lifetime?
Environmental factors Lifestyle factors Cell replication
36
Do all genetic changes that occur in a cell lifetime cause cancer development?
No, most changes are repaired but a few persist and develop into cancer
37
Why do more mutations occur with every stage of cancer development?
More mutations make the cancer more aggressive so that it can survive
38
How does a proto-oncogene mutate into an oncogene?
One allele of the proto-oncogene undergoes dominant driver mutation, which forms the oncogene
39
What are the 2 features of a protein expressed by an oncogene?
Increased activity No regulation
40
What type of mutation forms the philadelphia chromosome?
Translocation
41
What genes are involved in formation of the philadelphia chromosome?
ABL proto-oncogene of chromosome 9 and BCR proto-oncogene of chromosome 22
42
What fusion gene in formed in the philadelphia chromosome?
ABL-BCR oncogene
43
What is the cancerous effect of the philadelphia chromosome?
Uncontrollable division, as ABL-BCR fusion gene is always switched on
44
How does the MYC proto-oncogene mutate in cancer?
Amplifies to form multiple copies of the MYC oncogene
45
What is amplification of genes?
Same gene has 10-100 copies in the genome
46
What is the cancerous effect of the MYC oncogene being amplified?
Increases expression of protein
47
How does the RAS proto-oncogene mutate in cancer?
Point mutation (affects single base)
48
What is the effect of the RAS oncogene on the expressed protein?
It has different amino acid sequence, so has different functionality
49
How is leukaemia subclassified in terms of disease course?
Acute or chronic
50
How is Leukaemia subclassified in terms of predominant abnormal cell type?
Lymphoid or myeloid
51
How is Leukaemia subclassified in terms of genetic changes?
eg. Translocation, DNA mutation
52
What is the normal role of TS genes?
Restrain uncontrollable cell division by activating DNA repair mechanisms or apoptosis in response to DNA damage
53
What kind of cancers can TS gene mutations be associated with?
Rare familial cancers
54
What mutation occurs in each TS allele in cancer cell phenotype?
One allele undergoes germline mutation or deletion One allele undergoes deletion or inactivation
55
What chromosome is the RB gene on?
Chromosome 13
56
What cancer is caused by loss of both copies of the RB gene?
Retinoblastoma, retina tumour in children
57
What are the 2 forms of retinoblastoma?
Sporadic and inherited
58
In the sporadic form of retinoblastoma, what mutations occur?
Both RB genes undergo somatic (not passed on) mutations
59
In the inherited form of retinoblastoma, what mutations occur?
One RB gene undergoes germline (passed on in sperm/ovum) deletion Other RB gene undergoes somatic mutation
60
What is the function of the TP53 gene?
Instructs how to synthesise p53 protein
61
Why is p53 called the 'guardian of the genome'?
Regulates cell-cycle and division to prevent tumour development
62
In what percentage of all cancers is TP53 inactivated?
40%
63
What is Li-Fraumeni syndrome?
Rare autosomal disorder caused by inherited TP53 mutation
64
How does familial clustering occur in Li-Fraumeni syndrome?
Familial clustering of early onset tumour (before age 45)
65
Give 4 types of tumour that are predominant in Li-Fraumeni syndrome?
Sarcomas Breast cancers Brain cancers Adrenocortical carcinomas
66
What is the approximate ratio of individuals with Li-Fraumeni syndrome worldwide?
1 in 5000 to 1 in 20,000
67
What percentage of people with Li-Fraumeni syndrome develop cancer by age 40?
50%
68
What percentage of people with Li-Fraumeni syndrome develop cancer by age 60?
90%
69
What is the percentage risk of females with Li-Fraumeni syndrome developing cancer in their lifetime and why?
Nearly 100% risk due to increased risk of developing breast cancer
70
How many cancers do many individuals with Li-Fraumeni syndrome develop during their lifetime?
2 or more primary cancers
71
What percentage of all UK deaths does cancer cause?
28%
72
What percentage of people are diagnosed with cancer in their lifetime in the UK?
50%
73
What is a germline mutation?
Detectable variation in genome of germ cell (reproductive cell in foetus), that is passed onto offspring when the mutated oocyte/sperm forms a zygote
74
Can germline mutations increase familial risk of cancer?
Yes, this is seen when there is a family history of cancer
75
What 2 procedures can patients with potential germline mutations have?
Additional screening Preemptive treatment
76
What 2 genes can have germline mutations that develop ovarian and breast cancer?
BRCA1, BRCA2
77
What 2 preemptive treatments can women with BRCA1 and BCRA2 have?
Mastectomy (surgical removal of one/both breasts) Oophorectomy (surgical removal of one/both ovaries
78
What is a somatic mutation?
Random genetic change in cell after fertilisation, so can't be passed onto offspring as it doesn't involve germline
79
What is the difference between initiator carcinogens and promoter carcinogens?
Initiator carcinogens predispose cells to cancer development, but promoter carcinogens stimulate cancer development
80
What are the 3 most preventable causes of cancer from most preventable to least preventable?
Smoking (19% preventable cases) Obesity (7.8% preventable cases) Alcohol (5.6% preventable cases)
81
What kind of carcinogen is tobacco smoke?
Chemical
82
Give 4 examples of cancers that are associated with tobacco smoke?
Lung, mouth, throat, bladder
83
Give 3 examples of cancers that are associated with ionising radiation?
Leukaemia, skin, bone
84
Give 2 examples of cancers that are associated with sunlight?
Skin, lymphomas
85
How does age affect the likelihood of developing cancer?
Incidence of cancer increases with age
86
Give 1 example of cancer whose likelihood doesn't increase with age?
Testicular cancer
87
How can driver mutations explain why cancer incidence increases with age?
Several driver mutations need to occur over cell lifetime to develop into a cancer
88
How can oncogenes and TS genes explain why cancer incidence increases with age?
Up to 11 key changes in oncogenes or TS genes before cancer manifests
89
Why can cancers with familial risk take years to develop?
More genetic changes are needed for full expression to develop cancer
90
How many types of cancer is obesity associated with?
Up to 13
91
How does obesity lead to cancer development?
Fat cells synthesise extra hormones and growth factors, which signal to cell to divide more frequently, which increases chances of mutations occurring

Genetics (2 decks)

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