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Systems: Specialities AB > Genetics: Predisposition to Cancer > Flashcards

Genetics: Predisposition to Cancer Flashcards

1
Q

What is the human genome?

A

23 pairs of chromosomes made of 6,000 million base pairs forming 22,000 genes

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2
Q

How is extragenic DNA composed?

A
  • Repetitive sequences
  • Control regions
  • Spacer DNA between genes
  • Function mostly unknown
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3
Q

What do disease associated mutations do to DNA?

A

Alter protein function (protein is non-functional or missing)

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4
Q

How much breast cancer is hereditary

A
  • Family clusters= 15-20%

- Hereditary= 5-10%

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5
Q

How much ovarian cancer is hereditary?

A

5-10%

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6
Q

What are the causes of hereditary susceptibility to colorectal cancer?

A
  • Familial (10-30%)
  • Hereditary nonpolyposis colorectal cancer (5%)
  • Familial adenomatous polyposis (1%)
  • Rare CRC syndromes (<0.1%)
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7
Q

What are the stages in the cell cycle?

A
  • Mitosis
  • G1 (cell growth)
  • G0 (resting)
  • Synthesis
  • G2
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8
Q

Where do oncogenes act in the cell cycle

A

G1-G0

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9
Q

Where do tumour suppressor genes act in the cell cycle?

A

G0-S

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10
Q

Where do DNA repair genes act in the cell cycle?

A

S-G2

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11
Q

What are tumours?

A

Clonal expansions

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12
Q

What do cancers arise from?

A

Gene mutations

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13
Q

What are the features of germline mutations?

A
  • Mutation occurs in egg or sperm an affects all cells in the offspring
  • Are heritable
  • Cause cancer family syndromes
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14
Q

What are the features of somatic mutations?

A
  • Occur in nongermline tissues

- Are nonheritable

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15
Q

What role do oncogenes play in cancer development?

A
  • Normal genes (regulate cell growth)
  • Mutation in 1 gene leads to accelerated cell division
  • 1 mutation sufficient for role in cancer development
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16
Q

What oncogene is implicated in leukaemia?

A

Oncogene ABL coding for BCR-ABL fusion protein

17
Q

What role do tumour suppressor genes play in cancer development?

A
  • Normal genes prevent cancer
  • 1st mutation makes you a susceptible carrier
  • 2nd mutation/loss leads to cancer
18
Q

Using colon cancer, give an example of multi-step carcinogenesis.

A 
Normal epithelium
LOSS OF APC
>Hyper-proliferative epithelium
>Early adenoma
ACTIVATION OF KRAS
>Intermediate adenoma
LOSS OF 18Q
>Later adenoma
LOSS OF TP53
>Carcinoma
OTHER ALTERNATIONS
>Metastasis
19
Q

What is DNA mismatch repair?

A
  • Sometimes there is a base pair mismatch i.e. A+G
  • Normal DNA repair will lead to A+T
  • Mutations can be introduced by unrepaired DNA
20
Q

What are the features of Hereditary Non-Polyposis Colon Cancer (Lynch Syndrome)?

A
  • Mutation in mismatch repair genes
  • Excess of colorectal, endometrial, urinary tract, ovarian and gastric cancers
  • Adenoma- carcinoma sequence for polyp formation
  • Great opportunity for prevention by colonoscopy
21
Q

What are the clinical features of HNPCC?

A
  • Early but variable age at CRC diagnosis (~45 years)

- Tumour site in proximal colon predominates

22
Q

What cancers and BRCA1+2 associated with?

A
  • Breast cancer 60%-80% (often early age at onset)
  • Second primary breast cancer 40%-60%
  • Ovarian cancer 20%-25% (1>2)
  • Males: increased risk of prostate cancer and breast cancer especially BRCA2
23
Q

What are the features of autosomal dominant inheritance?

A
  • Each child has 50% chance of inheriting the mutation
  • No “skipped generations”
  • Equally transmitted by men and women
24
Q

When should you suspect a hereditary cancer syndrome?

A
  • Cancer in 2 or more close relatives (on same side of family)
  • Early age at diagnosis
  • Multiple primary tumors
  • Bilateral or multiple rare cancers
  • Characteristic pattern of tumours (e.g. breast and ovary)
  • Evidence of autosomal dominant transmission
25
Q

The cancer family history is the key to…

A

-Accurate risk assessment
-Effective genetic counselling
0Appropriate medical follow-up

26
Q

What is involved in the cancer genetics process?

A
  • Obtain a detailed family history
  • Confirm diagnoses of cancer
  • Risk estimation
  • Explanation of basis of risk
  • Interventions
  • Counselling
  • Genetic testing considered if high risk
27
Q

How can surveillance for breast cancer be carried out?

A

Early clinical surveillance 5 years before the age of the 1st cancer in family

  • Annual or clinical breast exams
  • Mammography: (moderate-high 2 yearly 35-40 and yearly 40-50) (high 18 monthly 50-64)
  • MR screening those at highest risk
28
Q

What are the features of prophylactic mastectomy?

A
  • Removes most but not all breast tissue
  • Significantly reduces breast cancer risk in women with a family history
  • Total (simple) mastectomy removes more breast tissue than subcutaneous mastectomy
  • BRCA1 mutation-positive women breast cancer incidence reduced to 5%
29
Q

What are the features of prophylactic oophorectomy?

A
  • Eliminates risk of primary ovarian cancer; however, peritoneal carcinomatosis may still occur
  • Laparoscopic oophorectomy reduces postsurgical morbidity
  • Induces surgical menopause but HRT till 50 does not change BRCA risk
  • Risk of subsequent BRCA halved in mutation-positive women
30
Q

What is the surveillance for CRC?

A

Colonoscopy

  • High risk 2 yearly from 25
  • Moderate risk: at age 35 and 55
31
Q

What is the surveillance for endometrial cancer?

A
  • Look for PMB
  • Transvaginal ultrasound
  • Surgery
  • Debatable but not recommended
32
Q

What are the benefits of genetic testing?

A
  • Identifies highest risk
  • Identifies non-carriers in families with a known mutation
  • Allows early detection and prevention strategies
  • May relieve anxiety
33
Q

What are the risks and limitations of genetic testing?

A
  • Does not detect all mutations
  • Continued risk of sporadic cancer
  • Efficacy of interventions variable
  • May result in psychosocial or economic harm
34
Q

What is the future of genetic testing?

A
  • Polygenic risk scores to decide on screening in families without a highly penetrant mutation
  • Increasing role of germline and tumour genetic profile in determining treatment of cancer

Systems: Specialities AB (19 decks)

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