Metastatic breast cancer means the cancer has spread from your breast to distant organs such as your bones, lungs, or other parts of your body.
No matter where the cancer spreads, it's still called "breast cancer." For example, breast cancer that has spread to your lungs is called "breast cancer," not "lung cancer." Your doctor will still treat it like breast cancer.
Doctors sometimes use the term "advanced breast cancer" or "stage IV breast cancer" to describe cancer that has spread. Stage IV is the most advanced stage of the disease.
If your cancer has metastasized (another way to say "spread"), you might wonder what to expect. Metastatic breast cancer isn't curable, but it is treatable. Several treatments can slow its progress, relieve your pain and other symptoms, and help you live longer.
How Common Is It?
About 168,000 women in the United States live with metastatic breast cancer. Men can have metastatic breast cancer too, but it's rare.
Only about 6% of women with breast cancer are diagnosed at stage IV. About 20% to 30% of women who have metastatic breast cancer were first diagnosed with an early-stage breast cancer, and then the cancer spread.
How Breast Cancer Spreads
Cancer cells can travel from your breast to other organs through your lymph system or bloodstream. Often, breast cancer spreads when it gets into the lymph nodes under your arms (called axillary nodes). From there, it enters the lymphatic system, a collection of nodes and vessels that are part of your body's immune system.
Once the cancer has reached other organs, it forms new tumors.
Metastatic breast cancer can also start months or years after you've finished treatment for an earlier-stage cancer. This is called a distant recurrence.
Treatments like surgery, radiation, and chemotherapy are good at removing or killing cancer cells. But sometimes, they can leave a few cancer cells behind. Even a single cancer cell can grow into a new tumor that spreads to other parts of your body.
Where Breast Cancer Tends to Go
Breast cancer most often spreads to these organs:
Bones. Breast cancer travels to the bones through the bloodstream. The ribs, spine, pelvis, and long bones of the arms and legs are the most common bones that breast cancer reaches. Bone pain and tenderness are signs the cancer is in your bones. Breast cancer cells can also get into bone marrow -- the spongy tissue inside bones where blood cells are made.
Liver. Cancer cells can get into the liver through the bloodstream because the liver filters the blood.
Lungs. The lungs are another common site for metastatic breast cancer to spread because your blood flows through them to pick up oxygen.
Brain. Any type of breast cancer can spread to the brain, but HER2-positive and triple-negative cancers are most likely to reach this organ. Signs of cancer in the brain include headaches, seizures, vision changes, and dizziness.