Clinical Cancer Genetics Flashcards

1
Q

As a recap, what is DNA?

A

Deoxyribonucleic acid (DNA) is a molecule encoding the genetic instructions used in the development and functioning of living organisms.

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2
Q

As a recap, what are genes?

A

They are the instructions to tell the body how to grow, develop and function.

it consist of sections of DNA which the cell translates into proteins.

We have about ~20,000 genes in the human genome.
We have 2 copies of most genes – one on each chromosome.

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3
Q

Exapnd on genetic variation.

A

it is what makes us unique - “polymorphisms” .

It:

  • is the basis for evolution
  • is the basis for disease
  • is caused by intrinsic errors in DNA replication and repair
  • is also caused by external factors
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4
Q

In basic terms, what is cancer?

A

Normal cells divide, replicating their DNA before division.
DNA replication is complicated and can result in errors in a gene/s (i.e. a somatic mutation).

Normal cells die when an error cannot be repaired.
Cancer results when mutations accumulate, cell does not die and cell growth is uncontrolled.

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5
Q

What are some general cancer statistics?

A

Cancer is a common disease in humans.
There is a 1 in 2 lifetime risk of developing cancer.

Most cancers are caused by a combination of genetic, environmental and lifestyle factors – multifactorial/ sporadic.

Only ~5-10% of cancers are due to the inheritance of a single cancer susceptibility gene.

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6
Q

What is the difference between a germline mutation and a somatic mutation?

A

A germline mutation is either inherited or occurs at the point of conception. All the cells of the body will be affected.

A somatic mutation occurs after the point of fertilisation (at some point during development). Only certain cells in the body will be affected.

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7
Q

List some differences between sporadic and hereditary cancers.

A

SPORADIC CANCERS:

  • no increased risk of other cancers
  • usually small increased risk to relatives
  • no genetic testing indicated
  • normal clinical management for affected individuals

HEREDITARY CANCERS:
- high risks of recurrence/other associated cancers
- high cancer risks in relatives
We can offer testing to at risk individuals
- we can offer screening and preventative management to gene carriers
- may alter treatment of affected individuals

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8
Q

Exaplin Knudson’s “Two Hit Hypothesis” using the example of retinoblastoma.

A

For a retinoblastoma to develop, a cell needs to carry two faulty copies of the RB1 gene.

In hereditary retinoblastoma, if the sperm has a faulty RB1 gene, the fertilised egg has a 50% chance of inheriting the RB mutation.
Then, this mutation in one copy of the RB gene is inherited in all body cells. This gives it a higher chance of mutation of the second copy of the RB gene occuring in one or more retina cells.

In non-hereditary retinoblastoma, the fertilised egg inherits no RB mutation. Thus, both mutations of the RB gene need to occur spontaneously for the retinoblastoma to present, which may take longer.

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9
Q

What is penetrance in terms of cancer?

A

NOT every person with a germline mutation develops the disease; this is known as reduced penetrance.

We can give risks of developing disease for a given genotype:

  • based on family/ population studies
  • unknown modifying factors
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10
Q

Describe cancer susceptibility genes.

A

Different classes of genes are targeted in cancer, which function in normal cell regulation:

  • Growth promoting proto-oncogenes: e.g. RET in MEN2
  • Growth inhibiting tumour suppressor genes: e.g. RB1 in retinoblastoma
  • Genes involved in DNA damage repair: e.g. BRCA1 and BRCA2 genes in breast/ovarian cancer

Other mechanisms of oncogenesis:

  • Epigenetic mechanisms of oncogenesis
  • Chromosomal aberrations
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11
Q

Describe the basics of taking a family history.

A
  • take a 3 generation family history
  • ask about consanguinity
  • ask about ethnic background (for e.g. Ashkenazi Jewish, other founder populations)
  • ask about types and ages of all cancers

NB. Some individuals with a hereditary predisposition to cancer do not have a family history of cancer.

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12
Q

What are some decisions that can be made from taking a family history?

A

Is genetic testing indicated?
Or are other investigations required first?
- confirmation of cancer diagnoses
- testing of tumour samples (e.g. IHC)

Is increased screening indicated?

  • for affected individual
  • for unaffected relatives
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13
Q

What are some implications of undertaking genetic testing?

A

Implications for individual:

  • recurrence risks
  • risks of other cancers

Implications for relatives:

  • how to share information
  • concerns about children
  • predictive testing

Insurance implications:
- current moratorium for predictive testing

Family planning options (e.g. prenatal, PGD)

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14
Q

Describe the BRCA 1 and BRCA 2 genes.

A

BRCA1 mutations - 0.11% population
BRCA2 mutations - 0.12% population

Their function is in repair of double stranded DNA breaks (homologous recombination).

It is responsible for
~ 16% familial breast cancers
~ 5% breast cancer
~ 10% ovarian cancer (also prostate, pancreatic, fallopian tube and peritoneal cancers)

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15
Q

What screening c an be undertaken for BRCA carriers?

A

BREAST SCREENING:

  • 30-50y: annual MRI screening
  • 30-50y: annual mammograms
  • > 50: annual mammogram

OVARIAN SCREENING:

  • unproven efficacy
  • not currently recommended
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16
Q

What are risk-reducing options for women at risk of breast/ovarian cancer?

A

MASECTOMY:

  • most effective way of reducing risk - <5% over lifetime
  • avoids need for cancer treatment
  • can help women with anxiety
  • breast reconstruction available

BILATERAL SALPINGO-OOPHORECTOMY:

  • offered at age 40 or after completed family
  • can give HRT (hormone replacement therapy) under specialist guidance
  • only proven way to reduce ovarian cancer risk

ALTERED CLINICAL MANAGEMENT:

  • PARP inhibitors
  • as they have a sensitivity to platinum chemotherapies
17
Q

Describe HNPCC.

A
  • aslso knowsn as Lynch syndrome
  • there are germline mutations in DNA mismatch repair genes (MLH1, MSH2, MSH6, PMS2)

You get a hereditary predisposition to:

  • colorectal cancer
  • ovarian cancer
  • endometrial cancer
  • plus gastric, pancreatic, hepatobiliary tract, urothelial and small intestine cancers
18
Q

How would you screen for HNPCC?

A
  • a colonoscopy every 18-24 months, from age 25-30
  • discuss endometrial screening from age 35 (but not proven to be effective)
  • discuss option of risk-reducing TAH/BSO from early 40’s
19
Q

How would you test for Lynch syndrome?

A
  • Tumour testing on colorectal and endometrial cancers (IHC/MSI)
  • Gene panel testing for MLH1/ MSH2/ MSH6/ PMS2
20
Q

Describe the prophylactic management of Lynch syndrome.

A

Aspirin reduces cancer risk in Lynch syndrome patients by ~50%.

CAPP2 research study showed aspirin reduced risk of colorectal cancer.

CAPP3 research study is happening at the moment to determine efficiacies of 600mg, 300mg, and 100mg aspirin daily.

21
Q

List some other hereditary cancer syndromes.

A
  • Li-Fraumeni Syndrome (TP53 gene) (adrenocortical, sarcomas, childhood, breast) - highly penetrant (70-90% chance of cancer)
  • Renal cancer syndromes (VHL, FLCN, FH, MET)
  • Pheochromocytomas/ Paragangliomas (SDHB/C/D)
  • Multiple Endocrine Neoplasia Type 1 (MEN1)
  • Multiple Endocrine Neoplasia Type 2 (RET)
  • Retinoblastoma (RB1)
  • Neurofibromatosis Type 1 (NF1)
  • Neurofibromatosis Type 2 (NF2)
  • Tuberous Sclerosis (TSC1/TSC2)
  • Familial Adenomatous Polyposis (AFP)
  • MYH-associated Polyposis (MUTYH)
  • Peutz-Jeghers syndrome (STK11)
  • Cowden Syndrome (PTEN) (hyroid and breast cancers, macrocephaly)
  • Diffuse stomach cancer and lobular breast cancer (CDH1)
  • Familial melanoma (p16)