Clinical Cancer Genetics Flashcards
What can we do to reduce cancer in people at increased genetic risk?
Putting people in screening programmes to:
- prevent the cancer
- detect it early
What makes individuals different from one another?
Genetic variation
-may influence our chance of developing disease
Prevalence of cancer
Common disease:
-1 in 2 lifetime risk of developing cancer
Genetic Predisposition to Cancer
2/3rds of cancers are “sporadic”
1/3rd of cancers are genetic (inherited)
- a small proportion (~5-10%) are due to a single high risk genetic change in a cancer predisposition gene
- larger proportion due to the inheritance of multiple lower risk factors (familial)
Sporadic cancer arises from
acquired somatic mutations in cancer genes which “drive” the cell to become cancer
-NOT inherited changes
Inherited cancer arises from
genetic changes we are born with which increase the risk of developing cancer:
High Risk Changes
-cancer predisposition genes (very rare)
Moderate Risk Changes
Low Risk Changes
- more common
- e.g. SNPs/common variants
High Risk Genetic Changes: cancer predisposition genes
very rare in the population, but if you have one, you have a really high chance of developing cancer in your lifetime
Low Risk Genetic Changes
More common in the population. Having one low risk genetic change only increases risk of cancer by a small amount, but if you have many of them, they all add up and the risk increases (multifactorial/polygenic)
-e.g. SNPs/common variants
What does clustering of the same types of cancer in a family indicate?
Increased multifactorial risk of cancer (polygenic):
- SNPs more common in cases than in controls
- With these common variants your risk of developing cancer is pushed from the normal distribution
- Cases are on average at a higher prior risk of developing cancer than the normal population
What affects the likelihood of the cancer being due to a high risk cancer predisposition gene?
How likely you are to have a high-risk cancer predisposition gene depends on the type of cancer
Why identify patients with increased genetic predisposition to cancer?
- provides reason for why developed cancer
- Informs medical management and surgical options
- Informs patient about future cancer risks
- Informs relatives about cancer risk - access to screening/ risk reducing surgery
How do we assess inherited cancer risk?
- Take 3 generational family history
- Consider types of cancer to see if they increase chance of a high risk CPG
- Assess pathology
- Molecular testing
- Look for rare syndromic features which could indicate high risk CPG
- Use National Genomic Test Directory Eligibility Criteria to decide if genetic testing is indicated
Assessing inherited cancer risk: Family history assessment
Take 3 generation family history
- number of affected relatives
- age at which they got cancer (e.g. breast cancer rare under 40)
- types of cancer (e.g. whether there has been multiple cancer diagnoses of the same type in closely related individuals)
- ethnic origin- higher rate of CPG in some populations
- look at certain patterns for high risk CPG (e.g. breast and ovarian usually together in families)
Assessing inherited cancer risk: Pathology
Certain pathological subtypes of cancer are more likely to be due to high risk CPGs e.g.:
- High grade serous ovarian cancer (BRCA1/2)
- Medullary thyroid cancer (RET)
- Triple negative breast cancer (BRCA1/2)
- Type 2 papillary kidney cancer (FH)
Assessing inherited cancer risk: Molecular Testing
Tumour testing may identify genetic changes which could indicate inherited risk.
Need to check with a blood test:
- immunohistochemistry of mismatch repair genes in Lynch syndrome
- BRCA gene sequencing in ovarian cancer
Assessing inherited cancer risk: Syndromic Features
Trichilemmoma:
-specific skin lesion strongly associated with mutations in PTEN gene, which causes Cowden syndrome, which increases risk of thyroid, breast and womb cancer
Mucocutaenous Pigmentation :
- mutation in STK11 gene causing Peutz-Jeghers syndrome, which is associated with increased risk of breast cancer and bowel polyps
- indicates an inherited cause for a person’s cancer
Prevalence of breast cancer
Because breast cancer is very common (1 in 8 women), it is not unusual to see multiple cases of breast cancer at older ages (after 40) within a family. This would be a classic multifactorial/polygenic risk pattern. Not indicative of high risk gene predisposition because the people are a bit older and there are no other associated cancer types.
However, an unaffected person should be offered extra screening because they’ve got multiple other relatives who have had breast cancer.
How do we work out what screening women should get for breast cancer?
An algorithm is used to work out exactly what screening people should get:
Green Category (17-30% lifetime risk of breast)
- start annual mammograms at age of 40 until they are 49
- then a mammogram every 3 years
Yellow Category (>30% and deemed high risk of developing cancer)
- annual mammograms between 40 and 59
- then a mammogram every 3 years
Analysing family tree including multiple breast cancers
This family tree calls for more worrying because of the amount of breast cancer, the ages and the fact that it is linked with ovarian cancer.
This all points to high risk cancer predisposition genes (CPGs), and therefore genetic testing is done (e.g. BRCA testing).
Implications for individual if high risk CPG found:
- Recurrence risks
- Risks of other cancers
Implications for relatives if high risk CPG found:
- How to share information
- Concerns about children
- Family planning options (E.g. prenatal, PGD)
Cause of sporadic cancer
Sporadic Cancer→somatic mutations
· Occurs after division of the fertilised egg
· Only present in a subset of cells
· Not inherited from a parent
Cause of Hereditary Cancer
Hereditary Cancer→germline mutations +/- somatic mutations · Present in the fertilised egg · Present in every cell in the body · Can be inherited from a parent · Can be passed to offspring
Compare BRCA1 vs BRCA2
Case of breast cancer (pic)
Suspicions:
- Age of breast cancer (in 30s) which is unusual
- Pattern of breast cancer and ovarian cancer which fits with known breast and ovarian predisposition gene BRCA
- Also, tree shows many relatives with cancer
In this case, we would want to do a genetic test. We would do it in an affected person, preferably the person with breast cancer at the younger age.
Result showed there was a BRCA2 mutation. This allows to offer her treatment.
· Risk reducing bilateral mastectomy offered when being treated for cancer
· Allows us to test her sister
Management of those with a BRCA2 mutation (and hence CPG)
Screening:
-All women with a BRCA2 mutation should be having annual breast MRI for any breast tissue from the ages of 30-40. At the age of 40, we do a mammogram as well as the MRI until the age of 50. After 50, the women have annual mammograms.
Surgical Management:
- There is no good screening for ovarian cancer, and so recommendation for BRCA2 mutation carriers is that they have risk-reducing surgery of the fallopian tubes and ovaries. But because the risk is not increased until after 50 years of age, we recommend that about the age of 45.
- Risk reducing breast surgery can also be done (bilateral risk reducing mastectomy).
Chemoprevention:
-Chemoprevention for BRCA2 mutation carriers can also be undergone to reduce breast cancer risk if they are still having breast tissue.
