pathologic process metastasis The spread or migration of cancer cells from one part of the body (where they first appeared) to another. The secondary tumor contains cells that are like those in the original (primary) tumor. [ NCI ] cancer metastasis tumor cell migration A tumor formed by cells that have spread is referred to as a "metastatic tumor" or a "metastasis", but, strictly speaking, “metastasis” refers to the process of cancer cell migration, not to the tumor mass itself. MeSH:D009362 NCIt:C19151 MedDRA:10062194 neoplasm metastasis tumor metastasis