Genetic Testing and Cancer: What You Should Know

Germline genetic testing for hereditary cancer syndromes (in which a person has a higher genetic risk of developing certain cancers) has been available for over three decades. It started with the discovery that mutations in the BRCA1 and BRCA2 genes raise the risk of breast cancer. Since then, variants of these and other genes have been linked to several different types of cancer, including ovarian, pancreatic, and prostate cancer.

Meghna S. Trivedi, MD, a breast cancer specialist and co-leader of the Hereditary Breast and Ovarian Cancer Program at Columbia's Herbert Irving Comprehensive Cancer Center, explains how germline genetic testing can improve care.

If someone is diagnosed with cancer, how can genetic testing help?

People with certain gene variants are at higher risk for developing some cancers. In breast cancer, for example, about 5% to 10% of cases are due to a disease-causing variant of a gene inherited from a parent.

Doctors use medical guidelines to determine who should get genetic testing. The recommendation to have genetic testing takes into account an individual's personal history of cancer (including tumor type, stage, and age of onset), as well as family history of cancer. For instance, guidelines recommend genetic testing for people with male breast cancer, ovarian cancer, pancreatic cancer, metastatic prostate cancer, and early-onset breast or colorectal cancer, as well as those with a strong family history of cancer.

Identifying a gene variant associated with cancer (also called a pathogenic variant) could help the doctor determine which treatments—such as surgery, radiation, or medication—may work best. For example, a class of drugs called PARP inhibitors can be used to treat cancers associated with pathogenic BRCA1 and BRCA2 variants. Certain chemotherapy drugs that cause DNA damage may also be used to treat cancer in people who carry these BRCA1 and BRCA2 variants.

Carrying a variant that increases cancer risk may raise your risk for more than one type of cancer. Identifying such variants allows you to be proactive about managing and reducing that risk through screening, surgery, or medication.

Genetic testing can also be done on a tumor. Tumor genetic testing, or somatic testing, looks at the DNA in tumor cells to identify alterations that indicate which treatment may be beneficial. Many alterations identified through somatic testing occur randomly rather than being inherited, so they do not pose a risk for family members. But if the tumor's DNA reveals an alteration in a gene associated with increased cancer risk, it may raise a red flag and suggest that a patient should have germline testing.

If someone has a gene variant that raises cancer risk, could other family members have the same variant?

Everyone inherits one copy of a gene from each parent. If you carry a pathogenic variant in a gene, all your first-degree relatives—including parents, siblings, and children—have a 50% chance of carrying the same variant. The more distant the relative, the smaller the risk. For example, second-degree relatives (aunts and uncles, grandparents and grandchildren, nieces and nephews, and half-siblings) have a 25% chance of carrying the gene variant.

Knowing you carry a variant that increases disease risk gives you the opportunity to let family members know so they can be tested. If they do have the same variant, they can begin cancer screening and take additional steps to reduce their risk, such as preventive surgery or medications.

Who do I ask about getting genetic testing?

Ask your doctor to refer you to a genetic counselor, who will do pretest counseling, order the genetic testing, and provide counseling after the results return.

Given the growing prevalence of genetic testing in recent years, there has been a shift toward oncologists taking the lead by sending a patient's blood or tissue sample to a lab for genetic testing and then referring to a genetics counselor to help interpret the results. Using this approach for individuals with a cancer diagnosis can allow for faster testing (which can help guide treatment decisions) and involve fewer appointments.

In a recent Columbia study, we found that over 65% of patients with metastatic breast and prostate cancer and any stage ovarian and pancreatic cancer completed germline genetic testing, which is higher than prior reports. However, certain groups aren't making use of genetic testing, so our future work seeks to increase the rates of genetic testing among all eligible cancer patients.

Speak with your doctor to find out if genetic testing may be recommended for you.

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Meghna S. Trivedi, MD, MS, is a Herbert Irving Associate Professor of Medicine at the Columbia University Vagelos College of Physicians and Surgeons and co-leads the Hereditary Breast and Ovarian Cancer Program at Columbia's Herbert Irving Comprehensive Cancer Center.