Genetic Testing

What is Genetic Testing?

Genetic testing means an analysis of your blood and possibly tumour tissue which is looking for "hereditary cancer" caused by a known mutated gene inherited from one of your biological parents. Most cancers are termed "sporadic" in that they are caused by circumstances other than an inherited, mutated gene. Cancer occurring in several immediate family members diagnosed with unrelated cancers is termed "familial cancer" and it is not readily understood as to whether it was inherited or environmentally related.

The results of genetic tests are extremely important to you as well as to other members of your family in assessing your/their statistical risk of developing cancer and/or developing new cancers.

Much clinical work has been done in the development of unique chemotherapeutic drugs for patients with known genetic mutations.  The knowledge of whether you do or do not carry a genetic defect can be of significant importance to your treatment outcome.

How do I start?

If you (the patient) have one or more immediate family members with a history of cancer, start by getting a referral from your oncologist or surgeon to the nearest Cancer Genetics Program. Many of these programs are administered within a cancer treatment center or medical university.  If you are a family member, with more than one occurrence of cancer in your immediate family, ask your family doctor for a referral.

The next step in assessing whether or not genetic testing is appropriate for you is to prepare a "cancer family tree" including the relationship of every family member that has had cancer, the age at which they were diagnosed, their type of cancer and the outcome. A genetics counselor will review the data and assess its relevance to inherited genetic mutations.

In the case of ovarian cancer, geneticists are primarily looking for breast cancer or ovarian cancer cases within your family history.  Defective BRCA1 or BRCA2 genes account for the majority of inherited breast and ovarian cancer.

What's next?

If there are one or more "first degree" family members - defined as a mother and/or sister with breast cancer or ovarian cancer - along with your diagnosis of ovarian cancer, you will usually be encouraged to be genetically tested.  

The procedure is simple - a vial of blood is drawn and possibly a tissue sample from your original tumour sent to a tissue bank for analysis. The results can take 6-9 months to receive.

What do the results mean to me and my family members?

Both women and men can inherit the BRCA1 or BRCA2 genetic mutation. If your genetics test is positive in detecting deleterious mutations in the BRCA1 or BRCA2 genes, it does not necessarily mean that your siblings carry the same genetic defect. However, in certain circumstances where you do not carry the BRCA1 or BRCA2 defective gene, your siblings may test positively.

A very important outcome of a male or female having a BRCA1/2 gene mutation is that they may pass the mutation on to a daughter or son.

The following is a summary of the current understanding of what positive results mean in terms of the cancer risks:

Risks for WOMEN with a BRCA1 or BRCA2 mutation:

• approximately 45-65% lifetime risk of developing breast cancer (versus 11% in the general population)
• approximately 10-40% lifetime risk for developing ovarian cancer (in comparison to 1-2% in the general population)
• women who have already had breast cancer are also at increased risk of developing a second cancer within 10 years after their initial breast cancer diagnosis - a 35-45% risk of new breast cancer, and/or a 5-15% risk of ovarian cancer.

Risks for MEN with a BRCA1 or BRCA2 mutation:

• up to a 7% lifetime risk for male breast cancer (in comparison to less than 1% in the general population)
• approximately 25-35% lifetime risk for prostate cancer (in comparison to 12% risk in the general population), however the age at diagnosis seems to be at the usual ages seen in the general population

There is also evidence to suggest a slightly increased risk of colon, stomach and pancreatic cancer for both men and women who inherit a BRCA1 or BRCA2 gene mutation. BRCA2 mutations may also predispose one to a slightly increased risk for cancer of the gall bladder and bile duct, liver and melanoma.

If BRCA1/2 testing is done and a mutation that is known to cause damage to the gene is NOT found in either of these genes, this result would not completely rule out an inherited form of breast and/or ovarian cancer in a family and could be interpreted in several ways:

• the cancer history is caused by a mutation in a different gene that has not yet been discovered
• the cancer history is caused by a mutation in the BRCA1/2 gene(s) that our current testing methods are unable to detect
• the cancer history occurred due to other chance factors - lifestyle, environment etc. - and therefore not due to an inherited gene mutation.

I have the defective BRCA1/2 gene - what can I do to prevent another incidence of cancer?

Science is very close to having an accurate blood test for ovarian cancer - that would be of tremendous benefit to high risk women.

However, in absence of an infallible test for women at increased risk of breast and/or ovarian cancer due to their family history, there are various options for them in cancer prevention. They have the option of having their ovaries and fallopian tubes removed - known as prophylactic bilateral salpingo-oophorectomy - after child-bearing is complete. It is also known that a prophylactic mastectomy significantly reduces the risk of breast cancer in women at high risk.

The field of genetics is one of the most exciting and fast-moving areas of cancer research in our time.  The hope is for tumour testing and genetic mapping to point the way to successful, individualized treatments in the future.  No matter what your family history, I would strongly encourage you to be tested.  

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