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Genetic Testing
revised August 18, 2009
Hereditary cancer genetic testing is "not just another blood test".
Eligibility criteria have been established by the Hereditary Cancer Program to ensure a consistent and equitable approach. Our goal, within the scope of current resources, is to maximize the availability of appropriate genetic testing that has impact on the medical management of individuals and families in BC/Yukon.
To provide informed consent, genetic counselling is required prior to blood samples being accepted by the Hereditary Cancer Program for genetic testing.
Genetic testing can be a lengthy, complicated laboratory process. When criteria have been met to test a specific hereditary cancer gene, there are 2 primary approaches: index or carrier testing.
1) Index testing
- first gene test in the family
- usually offered to a person who has had cancer, so Urgent DNA Storage may be indicated if there is concern about the health status of a potential index case for a family
- goal is to confirm whether a specific gene is associated with the pattern of cancer in the family
- involves testing of entire gene(s) to try to identify a mutation that interferes with the gene function
- results may take many months
- expedited BRCA1/2 index testing is available on a limited basis
- results can confirm hereditary cancer but cannot rule it out:
- if a mutation is identified, the hereditary cancer syndrome is confirmed and carrier testing is available to family members. Children and siblings of the "index" case will have a 50% chance of having inherited the same mutation.
- if no mutation is identified, hereditary cancer is not ruled out. It is possible that a mutation exists but was not detected with current technology, or that another gene is associated with the family history of cancer. In some cases it is appropriate to followup by offering index testing to another affected family member.
- 10-15% of results are of uncertain clinical significance
2) Carrier testing
- available when a specific gene mutation is already confirmed in the family
- tests only for the presence/absence of that specific gene mutation
- result confirms carrier status and associated cancer risks, but cannot predict when/if the individual will develop cancer
- positive result - person has inherited an increased risk to develop specific types of cancer
- negative result - person did not inherit an increased risk but remains at population risk for common cancers
- family member genetic test report (if available) should be included with a referral for genetic counselling
Refer to information about a specific hereditary cancer syndrome for details about the genes involved.
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