When breast cancer metastasizes, that means it has spread to other places in your body outside of the breast. Whether the cancer spreads to the bones, lungs, liver, or another place, it is still considered breast cancer. This is because these metastases have the same type of cancer cells as the primary cancer located in the breast.
MBC is sometimes referred to as advanced breast cancer or Stage 4 breast cancer. It is important to note that while “Stage 4 breast cancer” is commonly used interchangeably with “MBC,” the 2 terms do not always mean the same thing. The stage is determined at or soon after diagnosis, based on whether the cancer is limited to 1 area of the breast or whether it has spread to other areas or organs at said time. Over the course of the disease, your stage will most likely remain the same, even when the disease becomes metastatic. This means that you can have Stage 2 breast cancer and still have metastatic disease.