Definition: (meh-TAS-ta-sis): Plural: metastases (-seez) Slang: mets. The spread of cancer from one part of the body to another. Tumors formed from cells that have spread are called secondary cancer (tumors) and contain cells that are like those in the original (primary) tumor. Prostate cancer that has metastasized to (for example) bone is not bone cancer, but metastasized prostate cancer as they are still prostate cancer cells, no matter their location. See skeletal related event.
More information is at this site about bone metastases.