Metastasis

Metastasis, or metastatic disease, is the spread of a cancer or other disease from one organ or part to another not directly connected with it. The new occurrences of disease thus generated are referred to as metastases /mə ˈtæs tə siːz/ (sometimes abbreviated "mets"). It was previously thought that only malignant tumor cells and infections have the capacity to metastasize (also spelled metastasise); new research has caused this to be reconsidered. The existence of metastatic cancers in the absence of primary tumors also suggests that metastasis is not always caused by malignant cells that leave primary tumors.Metastasis is a Greek word meaning "displacement", from μετά, meta, "next", and στάσις, stasis, "placement".

Cancer occurs after a single cell in a tissue is progressively genetically damaged to produce cells with uncontrolled proliferation. This uncontrolled proliferation by mitosis produces a primary heterogeneic tumour. The cells which constitute the tumor eventually undergo metaplasia, followed by dysplasia then anaplasia, resulting in a malignant phenotype. This malignancy allows for invasion into the circulation, followed by invasion to a second site for tumorigenesis.