Cancer may spread from the site where it originated to other parts of the body. When cancer cells move away from a tumor, they may travel through the bloodstream to distant organs. If they travel through the lymph system, the cancer cells may end up in lymph nodes. The lymph nodes in the underarm are the first-place breast cancer is most likely to spread. Your doctor may perform a biopsy to check for the presence of cancer cells. The sample is examined by a pathologist who checks the nodes under a microscope. That exam determines lymph node status.
The spread of cancer to another part of the body is called metastasis. If breast cancer has metastasized to other areas of the body, it is categorized as stage IV breast cancer. Typically, breast cancer metastasizes primarily to the lungs, liver, brain, regional lymph nodesand bone.