Breast Cancer and Genetic Testing

Medically Reviewed by Sabrina Felson, MD on October 16, 2021

Women with a family history of breast cancer make up about 15% of all women with the disease. Having a close relative (mother, sister, or daughter) with breast cancer doubles your risk.

Breast Cancer Genes

Each cell in your body has about 20,500 genes. Genes are tiny segments of DNA that control how cells function. One copy of each gene comes from your mother. The other is from your father.

Genes can develop changes (also called abnormalities or mutations) that change how the cell works.

Mutations in two genes -- BRCA1 and BRCA2 -- are the most common causes of hereditary breast cancer, accounting for about 20% to 25% of cases.

Usually, BRCA genes help prevent cancer by fixing DNA damage that can lead to cancers and tumors. They also make proteins that help stop tumors from growing.

If either of your parents carries one of these mutations, you have a 50% chance of having it. And if you have it, you can pass it on to your children. If you inherit a mutated BRCA1 or BRCA2, you have higher odds of getting cancer.

Know the Risks

Women who inherit the mutated BRCA1 gene have a 55% to 65% risk of breast cancer by age 70. Women with mutated BRCA2 have about a 45% risk. Men with a BRCA mutation are also at a higher risk of breast cancer.

Either mutation brings a higher risk of getting breast cancer at a younger age (before menopause).

People who have a mutated BRCA1 or BRCA2 gene have a higher risk of a second primary breast cancer, too. Bilateral breast cancer (cancer in both breasts) is also more common in women who carry a BRCA 1 or BRCA2 gene.

These mutations also raise your risk of ovarian cancer, fallopian tube cancer, peritoneal cancer, and pancreatic cancer. Men face a higher risk of prostate cancer.

Should I Be Tested for Genetic Mutations?

At-risk families can take blood tests to look for mutations in these genes.

You may want to discuss genetic testing with your doctor if:

  • You have two or more blood relatives -- mother, sister, aunt, cousin, or daughter -- with premenopausal breast cancer or ovarian cancer diagnosed at any age.
  • You were diagnosed with breast cancer, especially before menopause, and have a blood relative with breast or ovarian cancer.
  • You were diagnosed with ovarian cancer and you have blood relatives who have had ovarian or breast cancer.
  • A male in your family has or had breast cancer.
  • You or a family member has been diagnosed with bilateral breast cancer (cancer in both breasts).
  • You were diagnosed with triple-negative breast cancer before the age of 60.
  • You are related to someone (male or female) who has a BRCA1 or BRCA2 mutation.
  • You are of Ashkenazi Jewish descent and have had breast or ovarian cancer or have blood relatives who have had breast or ovarian cancer.

Before Genetic Testing

Counseling is required before undergoing genetic testing for breast cancer. During this educational session, a health care provider will explain the benefits and risks of genetic testing and answer any questions you may have.

You’ll also have to sign a consent form. It’s an agreement between you and your health care provider, showing that you have discussed the tests and understand how the results might affect you and your family.

Here are some questions to consider when thinking about genetic testing:

  • Am I prepared to cope with the result? Are my family members also prepared, including my children and my spouse?
  • What are my goals for testing?
  • How would I use my test results? What will I do differently if the results are positive or negative?
  • With whom will I share my results?
  • Would a positive test result change relationships with my family?

What Happens During Genetic Testing?

You'll need a family pedigree to learn whether there is a cancer development pattern in your family. A family pedigree is a chart that shows the genetic makeup of a person's ancestors. It’s used to analyze characteristics or diseases that are passed down through a family.

Then, you’ll have a blood test to learn whether you have a breast cancer gene. Keep in mind that the vast majority of breast cancer cases are not linked with a breast cancer gene. In addition, scientists do not know all of the genes that can cause breast cancer, so they can test you only for the known genes.

When someone with a cancer diagnosis and a family history of the disease is found to have an altered BRCA1 or BRCA2 gene, the family is said to have a "known mutation." If there’s a link between the development of breast cancer and a breast cancer gene, then all family members willing to have genetic testing are asked to give a sample of blood. For many people, knowing their test results is important because this information may help to guide health care decisions for themselves and their families.

How Do I Interpret the Genetic Test Results?

A negative genetic test means that a breast cancer gene mutation was not identified. If other genetic testing has identified a mutation in your family, a negative test means you do not have the specific mutation. Therefore, your risk of cancer is the same as someone in the general population who has a family history of breast cancer.

If a BRCA1 or BRCA2 mutation has not been previously found in your family, a negative result should be interpreted cautiously. There is still a chance that you may be at higher risk for breast cancer because of changes in genes other than those that doctors can test for.

A positive test result means that a mutation known to raise the risk of breast and ovarian cancer was identified.

What Are My Options if I Have a 'Cancer Gene'?

Women in high-risk categories (first-degree relative with breast cancer, previous abnormal breast biopsy results with atypical ductal hyperplasia or lobular hyperplasia or lobular carcinoma in situ) and those who have the genes linked with breast cancer should consider starting regular breast cancer screening at age 25, or 10 years earlier than the age of the youngest relative with breast cancer at the time of their diagnosis.

Get to know how your breasts look and feel. If you notice any changes, see your doctor right away. And talk with your doctor about blood tests, pelvic exams, and transvaginal ultrasound to look for ovarian cancer.

Some women choose to have a preventive (prophylactic) mastectomy to lower their chances of breast cancer. It’s also possible to have your ovaries and fallopian tubes taken out. This doesn’t get rid of all risk, but it does significantly lower it.

Another approach includes using anti-estrogen drugs:

  • Tamoxifen, useful in premenopausal and post-menopausal women
  • Raloxifene (Evista), used to treat osteoporosis; useful only in post-menopausal women
  • Exemestane (Aromasin), an aromatase inhibitor; useful only in post-menopausal women

What Are the Potential Problems With Genetic Testing?

Genetic testing is not 100% accurate. If a test is negative, a person still has a chance of getting breast cancer. If the test is positive, there is still a 15% to 20% chance of not getting breast cancer.

Genetic testing is costly, ranging from about $400 to more than $3,000, depending on the type of test. Insurance coverage varies.

The results of genetic tests won't be available for several weeks. The length of time it takes to get results depends on the tests performed and under what circumstances they are done.

Genetic testing is very controversial. Legislation has been enacted to protect people who may have a documented genetic risk of cancer from employment or insurance problems. The best thing you can do is to become involved with an established genetic registry that can counsel people who have a genetic risk for cancer.

What Are the Benefits of Genetic Testing?

For some women, genetic testing may help you make informed medical and lifestyle decisions while easing the anxiety of not knowing their genetic background. You can also make a decision regarding prevention, with both medications and prophylactic surgery. In addition, many women take part in medical research that, in the long run, may lower their risk of death from breast cancer.

What About My Privacy?

The Health Insurance Portability and Accountability Act (HIPAA) of 1996 prevents insurance companies from denying coverage based on genetic information. This act also prevents insurance companies from using genetic information to determine that a health condition existed before application was made for insurance. In addition, many states have passed laws, or have legislation pending, addressing insurance concerns.

Show Sources


National Breast Cancer Coalition.

The American Cancer Society: "Breast cancer risk factors you cannot change,” "Genetic Testing: What You Need to Know,” “Can Ovarian Cancer Be Prevented?” “American Cancer Society Recommendations for the Early Detection of Breast Cancer.”


National Comprehensive Cancer Network.

NIH: "An Overview of the Human Genome Project." “Risk of Developing Breast Cancer.”

Mayo Clinic: “BRCA gene test for breast and ovarian cancer risk.”

National Breast Cancer Foundation: “BRCA: The Breast Cancer Gene.”

National Cancer Institute: “BRCA Mutations: Cancer Risk and Genetic Testing.”

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