Genetic testing for breast cancer: What the results mean

Before you undergo genetic testing to estimate your breast and ovarian cancer risk, consider what it might mean to get a positive or a negative test result.

Genetic testing is a way to estimate your cancer risk. But it's not for everyone. If you have a family history of breast or ovarian cancer, or if you have a relative who has tested positive for a BRCA1 or BRCA2 mutation, genetic testing may be in order.

If you're considering genetic testing, you might be thinking ahead to the test results. Does a negative test mean you're home free? What are your options if the test comes back positive? If, ultimately, you choose to undergo genetic testing, be prepared for what the test results might mean for you and your family.

Positive test results

If the test results come back positive, it means that you have a mutation in one of the breast cancer genes, BRCA1 or BRCA2. Identification of a BRCA mutation means you're at much higher risk of developing breast or ovarian cancer compared with someone at average risk of developing these cancers.

What should you do to reduce your risk? It's up to you. Many factors carry weight in the decision — your age, medical history, prior treatments, past surgeries and personal preferences. Take plenty of time to weigh your options.

"There's no urgency to act upon a positive result," says Sandhya Pruthi, M.D., a breast health specialist at Mayo Clinic, Rochester, Minn. "Allow yourself time for discussions with a genetic counselor and a breast specialist or oncologist. For some women, the decision to proceed with one option over another may happen within three months. For others, it may take six months to a year."

If your test results are positive, you may feel anxious, depressed or angry. But you may also find relief from the uncertainty of not knowing your risk status. Being fully informed allows you to make the best decisions about your future — and what steps you can take to reduce your cancer risk.

After a positive test, your risk-reducing options include:

Monitoring (surveillance). Surveillance for breast cancer means having clinical breast exams and mammograms at least once a year. Monthly breast self-examination also is a good idea — it will give you a sense of breast familiarity, which can help you detect any changes in your breasts.

If you have a BRCA mutation, it's recommended that you have more frequent clinical breast exams, such as every six months, and screening mammograms yearly. Your doctor may also recommend additional imaging methods, such as ultrasound or magnetic resonance imaging, as a part of your routine surveillance.

Surveillance for ovarian cancer includes having an annual or semiannual pelvic exam, transvaginal ultrasound imaging and a blood test to measure your cancer antigen 125 levels.
Medication (chemoprevention). Chemoprevention is the use of drugs to reduce your risk of cancer. Tamoxifen (Nolvadex) administered for a period of five years is currently the regimen most commonly used to reduce breast cancer risk in high-risk women. Raloxifene (Evista) — a drug used for preventing and treating osteoporosis — has been found to be as effective as tamoxifen in clinical studies. Other types of drugs also are being investigated as chemoprevention for breast cancer, including exemestane (Aromasin) — an aromatase inhibitor that reduces the amount of estrogen in your body. If you have a BRCA1 or BRCA2 mutation, your chemoprevention options may be limited, however. It's unclear how effective tamoxifen and raloxifene may be for preventing cancers in women with genetic mutations.
Preventive surgery. Preventive (prophylactic) mastectomy — the removal of healthy breast tissue — can reduce the risk of breast cancer by about 90 percent. Removal of healthy fallopian tubes and ovaries (preventive salpingo-oophorectomy) reduces the risk of breast cancer by 50 percent in premenopausal women, and it reduces the risk of ovarian and peritoneal cancers by more than 90 percent in both pre- and postmenopausal women.

However, preventive surgery doesn't eliminate all cancer risk. It's possible that cancer still might develop in the tissue that couldn't be removed through surgery. Preventive surgery is usually reserved for a high-risk woman with a hereditary predisposition for carrying a gene mutation or with a known BRCA1 or BRCA2 mutation.

Doctors are increasingly recommending estrogen therapy for premenopausal women who choose preventive oophorectomy. This entails taking the lowest effective dose of estrogen until about age 50, when most women would naturally enter menopause, to offset menopausal symptoms and prevent certain diseases, such as osteoporosis. Researchers discovered increased death rates, especially due to estrogen-related cancers and diseases of the brain and cardiovascular system, among younger women who underwent preventive oophorectomy and who weren't given estrogen after the surgery until at least age 45.

Negative test results

A BRCA test result is a true negative only if it finds that you don't carry a specific BRCA mutation already identified in a relative of yours. In that limited circumstance, "negative" means your risk of breast and ovarian cancer is the same as that of the general population.

In any other situation, though, a negative test result doesn't put you in the clear. You may still be at high risk of hereditary breast cancer if your family carries a high-risk gene mutation that hasn't yet been identified. As a result, you and your family may still need more rigorous screening. The BRCA1 and BRCA2 genetic test can detect the majority of gene mutations, but it's possible, if you receive a negative result, that the test was unable to detect your family's gene mutation. If no one in your family has a BRCA mutation, studies of families similar to your own may help your doctor or genetic counselor estimate your risk, but with a greater margin of error.

If you have a negative result — after one of your family members tests positive — you may feel like a huge weight has been lifted off your shoulders. You won't have to undergo more frequent screening or consider surgery or other preventive measures. Conversely, testing negative for a BRCA mutation may bring on feelings of guilt — especially if other family members do carry the mutation and face an increased cancer risk.

Many questions, few answers

Much remains to be learned about BRCA mutations. So far, nearly 2,000 mutations have been identified on the BRCA1 and BRCA2 genes. But not all of these genetic mutations carry the same risk of cancer. The level of risk associated with each BRCA mutation is unknown.

Having an altered BRCA gene doesn't mean you'll definitely get breast or ovarian cancer. Test results can't determine your exact level of risk, at what age you may develop cancer, how aggressively the disease might progress or how your risk of death from cancer compares with other women's risk.

If genetic testing reveals that you're at high risk of hereditary breast or ovarian cancer, many difficult decisions lie ahead. Further education and research, as well as discussions with your doctor or a genetic counselor, may make tough decisions somewhat easier.

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