Precision medicine for breast cancer is an approach to diagnosis, treatment and prevention that takes into account the genes you're born with (your genetic makeup) and the genes or others markers present within the cancer cells. With this approach, your blood or tumor tissue is collected for analysis, often genetic. The information may help predict or diagnose disease and guide treatment decisions.

Cancer care is among the first medical specialties to apply precision medicine. Several kinds of genetic and nongenetic tests for breast cancer are available that can help personalize therapy. Some genetic tests are specific to inherited risk, which means they look at your genetic makeup to determine your personal risk of developing breast cancer or other types of cancer in your lifetime. Inherited risk accounts for about 10 percent of all breast cancer cases.

Other tests check for genetic changes or variants (sometimes called mutations) within the cancer cells that help determine which treatments you'll most likely benefit from or if you need any treatments at all. For example, cells from a breast tumor may be tested to determine whether they produce too much of a protein called HER2. Someone with HER2-positive breast cancer is likely to respond to the drugs that target that protein. Some genetic tests will reveal whether your body will turn on (activate) certain medications thus helping to determine which treatment may be best for you.

Eventually, with new advances in precision medicine (also called individualized or personalized medicine) many more precise choices will become available.

The goal of precision medicine for breast cancer is to tailor treatment to your particular genetic makeup and the genetic changes in the cancer cells.

Precision medicine for breast cancer may involve analyzing the genetic makeup of your cells or, if you have cancer, the makeup of your cancer cells. Tests might include:

• Drug-gene testing. Your genes may influence the way your body processes medications, including those used to treat breast cancer. Your doctor may use information from a genetic test of your cells to determine which medications and dosages are most appropriate for you. The field of drug-gene interactions is called pharmacogenomics.
• Advanced cancer. If your cancer progresses despite treatment, your doctor might recommend testing the genetic makeup of your cancer cells. This test, called tumor sequencing, is used to look for changes or alterations in the cancer so that your doctor can choose the best drug for your type of tumor.
• Family history. Genetic testing for inherited gene mutations that increase your risk of breast cancer, such as the BRCA gene, is offered to people with a strong family history of the disease. Women who have these genes have an increased risk of developing breast cancer compared with the general population. This same test can also be used to determine if you would respond to a specific drug for the treatment of metastatic breast cancer (Parp inhibitor). Other, newer genetic tests may be available, too, depending on a person's family cancer history.