Breast cancer can often be cured when it is detected at an early stage, but some people experience disease progression despite treatment, and others are diagnosed after their cancer has already spread to other parts of the body, known as Stage IV, or metastatic breast cancer (MBC).
Experts estimate that around one quarter of women diagnosed with early breast cancer will progress to MBC, and about 10% have MBC as their initial diagnosis. Breast cancer is uncommon among men, but they are more likely to be diagnosed at a later stage. While it can’t be cured, some people live with MBC for years; the five-year survival rate is around 25%.
Cancer cells can break away from the original tumor and spread through the bloodstream or lymphatic system. MBC often spreads to the bones, liver, lungs or brain. Breast cancer that spreads to the liver, for example, is still considered breast cancer—not liver cancer.
Breast cancer is classified by the receptors on tumor cells. A majority of breast tumors carry estrogen or progesterone receptors and can be treated with hormone (endocrine) therapy. Others express a receptor called HER2 and can be treated with HER2 inhibitors. Triple-negative breast cancer doesn’t express any of these receptors, so it is harder to treat and more likely to spread. People with inherited BRCA mutations are more likely to develop MBC.
Unlike early breast cancer, the goal of MBC treatment is to prolong survival and maintain a good quality of life, rather than to completely eradicate it. Treatment depends on how advanced the cancer is and whether it has genomic biomarkers showing that certain medications are likely to work.
Surgery and radiation therapy may be used to shrink tumors and relieve side effects, such as pain due to bone metastasis.
Most people with MBC receive systemic medications that affect the whole body. Hormone therapy, such as aromatase inhibitors and selective estrogen receptor degraders, may be used to treat estrogen-receptor-positive MBC. Traditional chemotherapy works by killing fast-growing cells.
Targeted therapy works against cancer with specific characteristics. Antibody-drug conjugates, such as Enhertu (trastuzumab deruxtecan) and Trodelvy (sacituzumab govitecan), use antibodies to deliver potent drugs directly to tumors. CDK4/6 inhibitors—for example, Ibrance (palbociclib), Kisqali (ribociclib) and Verzenio (abemaciclib)—interfere with a kinase protein needed for cell division. PARP inhibitors, including Lynparza (olaparib) and Talzenna (talazoparib), block proteins that repair damaged DNA in people with BRCA mutations.
Immunotherapy helps the immune system fight cancer. Some tumors can turn off immune responses against them. Checkpoint inhibitors—Keytruda (pembrolizumab) and Jemperli (dostarlimab) are approved for MBC—can restore T cells’ ability to destroy cancer cells.
Hormone therapy, chemotherapy and targeted therapies can stop working, and immunotherapy doesn’t work for everyone. Because treatment is continually evolving, it is often possible to move on to new medications if the current ones are no longer effective. Integrative therapies, such as acupuncture, may help relieve symptoms or side effects. MBC treatment continues to improve, and several new therapies are currently under study. Ask your doctor whether a clinical trial might be a good option for you.