Breast cancer can remain localized in the breast, or it can spread throughout the body. When it spreads, it’s called metastatic breast cancer (MBC), or stage 4 breast cancer.

When breast cancer is limited to the breast and/or nearby lymph node regions, it is called early stage or locally advanced. When breast cancer spreads to an area farther from where it started to another part of the body, doctors say that the cancer has “metastasized.” They call the area of spread a “metastasis,” or use the plural of “metastases” if the cancer has spread to more than 1 area. The disease is called metastatic breast cancer. Another name for metastatic breast cancer is "stage IV (4) breast cancer” if it has already spread beyond the breast and nearby lymph nodes at the time of diagnosis of the original cancer.