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Principles of Medicine (POM) - Block 3 > Lecture 26: Cancer Genetics > Flashcards

Lecture 26: Cancer Genetics Flashcards

1
Q

What is a benign tumour?

A

A mass of well-differentiated cells that grows slowly, is capsulated and lacks the ability to invade neighbouring tissue or metastasize.

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2
Q

What is a malignant tumour?

A

Not self-limited in its growth (escapes apoptosis, able to produce new blood vessels), cells are poorly differentiated and capable of invading into adjacent tissues, and may be capable of metastasizing

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3
Q

How may cancer begin in terms of genetics?

A

Because of accumulation of mutations involving oncogenes, tumour suppressor genes and DNA repair genes

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4
Q

What is carcinogenesis?

A

the initiation of cancer formation

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5
Q

What are the 3 stages of carcinogenesis?

A

1) initiation - irreversible genetic alteration
2) promotion
3) progression

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6
Q

What is the microscopic appearance of cancer cells?

A
  • large no. of dividing cells
  • large, variably shaped nuclei
  • large nucleus to cytoplasm ratio
  • variation in size and shape
  • loss of normal cell features
  • disorganised arrangement
  • poorly defined tumour boundary
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7
Q

What are carcinomas?

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

What are sarcomas?

A
  • cancers arising from cells found in supporting tissues of body such as bone, cartilage, fat, connective tissue and muscle
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9
Q

What are lymphomas?

A
  • cancers that arise in the lymph nodes and tissues of the body’s immune system
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10
Q

What are leukaemias?

A
  • cancers of immature blood cells that grow in bone marrow and tend to accumulate in large numbers in bloodstream
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11
Q

What factors can cause cancer?

A
  • ENVIRONMENT: chemicals e.g. from smoking and radiation
  • EXOGENOUS: viruses introduce own genes into cells
  • GENETICS: rare and common, heredity, alterations in genes that make person more susceptible to cancer
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12
Q

What are the 6 hallmarks of cancer?

A

1) self-sufficiency in growth signals
2) insensitivity to anti-growth signals
3) tissue invasion and metastasis
4) Limitless replicative potential
5) Sustained angiogenesis
6) Evading apoptosis

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13
Q

What is meant by the hallmarks of cancer?

A

anti-cancer defense mechanisms that are hardwired into our cells, that must be breached by a cell on the path towards cancer

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14
Q

What are the 4 new hallmarks of cancer?

A
  • deregulating cellular energetics
  • avoiding immune destruction
  • tumour-promoting inflammation
  • genome instability and mutation
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15
Q

What is a germline mutation?

A

a mutation occurring in gametes and can be passed onto offspring (every cell in entire organism will be affected)

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16
Q

What is a somatic mutation?

A

occur in a single body cell and cannot be inherited (only tissues derived from mutated cell are affected)

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17
Q

Which type of mutation is more common - germline or somatic?

A

Somatic (90% of cancers) - germline is only 10% of cancers

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18
Q

Variations in which gene can lead to an increased risk for breast cancer as part of a hereditary breast-ovarian cancer syndrome?

A

BRCA1 gene

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19
Q

What percentage risk do females with an abnormal BRCA1 or BRCA2 gene have of developing breast cancer by age 90?

A

80%

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20
Q

Name some different types of mutation.

A
  • deletions
  • duplications
  • inversions
  • translocations
  • single base substitutions
  • chromosome instability
  • aneuploidy
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21
Q

What is a passenger mutation?

A

a mutation that doesn’t provide a selective advantage - - - defined as mutations that do not directly drive cancer initiation and progression, neutral, have no effect on fitness of a clone

22
Q

What is a driver mutation?

A

few mutations can confer a selective advantage and are recurrently found (in homozygote state) - drive cancer progression, cause clonal expansions

23
Q

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

A

How often stem cells in that tissue divide

24
Q

What is an oncogene?

A

A gene that has the potential to cause cancer - often mutated or expressed at high levels in tumour cells

25
Q

Most cancer-causing mutations involving oncogenes are…?

A

acquired, not inherited

26
Q

How can acquired mutations activate oncogenes?

A

By chromosome rearrangements, gene duplication, or mutation

27
Q

A chromosome rearrangement can lead to the formation of the gene BCR-ABL. What type of cancer can this lead to?

A

Chronic myeloid leukaemia (CML)

28
Q

What are RAS proteins?

A

Proteins belonging to the family of small GTPases which are activated in response to various extracellular stimuli

29
Q

What do RAS proteins control?

A
  • cellular signalling pathways responsible for growth
  • migration
  • adhesion
  • cytoskeletal integrity
  • survival and differentiation
30
Q

How do RAS proteins function?

A

As binary molecular switches that control intracellular signalling networks

31
Q

What is KRAS?

A

a gene that acts as an on/off switch in cell signalling. normally controls cell proliferation

32
Q

What happens when KRAS is mutated?

A

negative signalling is disrupted, cell proliferation no longer controlled

33
Q

What is a constitutive gene?

A

A gene that is transcribed continuously

34
Q

What can a constitutive Ras signal lead to?

A

Cancer

35
Q

Can mutations be inherited in proto-oncogenes?

A

Yes but it’s very rare

36
Q

What is a proto-oncogene?

A

A normal gene which, when altered by mutation, becomes an oncogene that can contribute to cancer.

37
Q

What is a tumour suppressor gene?

A

A gene that regulates cell during cell division and replication

38
Q

What can happen when a tumour suppressor gene is mutated?

A

It results in a loss or reduction in function which in combination with other genetic mutations could allow a cell to grow abnormally

39
Q

What was the first tumour-suppressor protein to be discovered?

A

retinoblastoma protein (pRb) in human retinoblastoma

40
Q

What is the two-hit hypothesis?

A

The hypothesis that most genes require two mutations to cause a phenotypic change. Inheriting one germline copy of a mutated gene is not enough to cause cancer but a second somatic mutation (2nd hit) to the good copy in the gene pair could produce cancer.

41
Q

What gene encodes the p53 tumour-suppressor protein?

A

TP53

42
Q

What functions does p53 have?

A
  • DNA repair
  • inducing apoptosis
  • transcription
  • regulating cell cycle
43
Q

What percentage of cancer diagnoses each year involved p53 mutations?

A

37%

44
Q

Loss of the TP53 gene occurs in what percentage of human cancers?

A

> 50%

45
Q

How are cancer cells without the TP53 gene genetically unstable?

A

They are unable to:

  • stop cell cycling to allow time for DNA repair
  • carry out efficient DNA repair
  • undergo apoptosis
46
Q

What do DNA repair genes code for?

A

Proteins whose normal function is to correct errors that arise when cells duplicate their DNA prior to cell division

47
Q

What factors affect the rate of DNA repair?

A
  • cell type
  • cell age
  • extracellular environment
48
Q

What 3 states can a cell that has accumulated a large amount of DNA damage or one that no longer effectively repairs it DNA enters?

A
  • an irreversible state of dormancy
  • cell suicide (apoptosis)
  • unregulated cell division –> lead to cancerous tumour
49
Q

How can viral infections lead to cancer?

A

DNA in virus can mix with cell’s DNA which can trigger changes in cell to make it grow and multiply

50
Q

What is an example of a cancer caused by a virus?

A

Cervical cancer caused by human papilloma virus (HPV) - responsible for 99.7% of cervical cancer

51
Q

Give an example of how bacteria is linked with cancer.

A

Helicobacter pylori has been associated with development of stomach cancer

Principles of Medicine (POM) - Block 3 (11 decks)

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