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Genetic testing: the benefits, the risks, and the latest knowledge

What is genetic testing?

According to Genetics Home Reference, “Genetic testing is a type of medical test that identifies changes in chromosomes, genes, or proteins. The results of a genetic test can confirm or rule out a suspected genetic condition or help determine a person’s chance of developing or passing on a genetic disorder1.”

How is a genetic test done?

A sample of blood, saliva, hair, skin, or other tissue is sent to a laboratory for analysis.  The laboratory then looks at the DNA, chromosomes, genes, and proteins and sends a written report to the doctor or genetic counsellor, or directly to the patient, depending on the test and who requested it.

How can genetic testing inform treatment decisions?

For breast cancer patients, genetic testing may help your oncologist understand whether you may respond better to one treatment over another. Mutations of several genes, including BRCA1 and BRCA2, are linked to breast cancer. Certain newer treatments have shown to be most effective for patients with BRCA-mutations.  If you have a BRCA mutation, your oncologist may recommend a different course of treatment than if you didn’t have the mutation. Something to consider is that if you test positive for hereditary germline mutations, like BRCA, this result may lead other family members to be tested as well. 

Healthy individuals who don’t have breast cancer but who have breast cancer-related mutations may decide to undergo a prophylactic mastectomy or may choose increased screening by mammogram or MRI at an earlier age than normal-risk patients would.  Drugs such as tamoxifen may also be given.

What are the implications of genetic testing for BRCA treatments?

Studies have shown differences in breast cancer patients with and without BRCA mutations.  For example, people with BRCA mutations have a higher risk of recurrence, and so a bilateral mastectomy is recommended. BRCA mutations can also impact the types of chemotherapy that might work best for you. Hormone receptor-negative BRCA1 mutated breast cancers are shown to be less sensitive to types of chemotherapies called taxanes2.  In one study, platinum agents such as cisplatin were also more effective in BRCA1 mutation carriers; doxorubicin and docetaxel were much less effective2. PARP inhibitors, a type of targeted therapy, can also be useful for some breast cancers with BRCA mutations.

What provinces and territories cover genetic testing for breast cancer patients?

In Canada, publicly funded genetic testing is restricted to those who meet certain high-risk criteria, such as a family history of breast cancer or early onset of the disease.  Click on your province or territory to find the criteria for your location:

What evidence is there that all breast cancer patients should be tested?

The American Society of Breast Surgeons recommends that all breast cancer patients undergo genetic testing.  This recommendation is based on a 2018 study that found that “patients with breast cancer who met NCCN (National Comprehensive Cancer Network) testing criteria had similar rates of pathogenic or likely pathogenic hereditary mutations (9 percent) as those who did not meet the NCCN criteria (8 percent)3.”

What if I don’t qualify for genetic testing that is covered publicly?  Can I pay for a genetic test somewhere else?

Two American direct-to-consumer genetic tests look at breast cancer and are considered to be credible; they also provide access to genetic counsellors who can help explain the test results, which is important.

Color offers a “thorough look at 30 genes to better guide a screening and prevention plan for breast, ovarian, uterine, colon, melanoma, pancreatic, stomach, and prostate cancers4.”  The test is $245 USD, which includes genetic counselling by phone.

Invitae “looks at 61 genes to assess your risk of developing an inherited form of cancer5.”  This test is $250 USD, which also includes genetic counselling by phone.

How can consumers be confident that a genetic test is valid and useful?

Direct-to-consumer genetic tests are not regulated in Canada, so it’s up to consumers to do their own research.  Many of the tests sold over the Internet have not undergone clinical evaluation, and are often for recreational purposes, not medical ones.  The Canadian Medical Association has a policy that raises many important considerations, including privacy, validity, and accuracy6.  Click here to read more about privacy concerns.

In the United States, most direct-to-consumer genetic tests are also not regulated, and the claims of the seller are often not independently verified7.  Another well-known company that offers genetic testing has approval from the Food and Drug Administration to offer direct-to-consumer testing for three variants on the BRCA1 and BRCA2 genes.  However, the results of this test may not be meaningful, since there are more than 1800 other variants that are not included in the test.  A New Brunswick resident, Victoria Boer, tested negative for BRCA variants in this popular test but subsequently tested positive in a more comprehensive test performed by IWK Health Centre in Halifax.  If she had not had the second test, she would not have received the correct information about her potential for developing breast cancer8.

Conclusion

Genetic testing has benefits as well as limitations and risks.   Before undergoing testing, make sure you understand the value and limits of a particular test.  A genetic counsellor can help by discussing the pros and cons of testing and offering emotional support and resources should the test prove positive for a cancer-related mutation.