A metastasis refers to a lump of cancer cells that’s physically separated from the original tumor. A metastasis can be local, like when colon cancer spreads to a nearby lymph node in the gut, or distant, as when lung cancer cells generate tumors in the adrenal gland, liver, bone or brain.
Sometimes metastases cause serious damage in the organs where they’ve settled. For instance, brain “mets” can result in impaired thinking, personality changes, blindness or seizures. Liver metastases, if large enough, can result in hepatic (liver) failure. Bone mets can lead to anemia and other blood cell deficiencies if the marrow becomes filled with malignant cells instead of normal ones.
A common source of confusion is that when cancer moves from one body part to another, it’s still referred to by its site of origin. For example, if breast cancer spreads to the liver or bone, it is still called breast cancer and most often treated as such. In general it’s the type of malignant cell, rather than the affected organ, that guides therapy.
Notes on usage: The plural is “metastases.” When someone has metastatic disease, that means their cancer has spread from the primary site to another. Oncologists don’t usually apply these terms to leukemia or lymphoma.