The plural of metastasis is metastases.
Metastasis refers to the spread of cancer cells from the original site (primary tumor) to other parts of the body through the lymphatic system or bloodstream. It is a critical stage in the progression of cancer and can affect various organs or tissues, forming secondary tumors or metastases. Metastasis plays a significant role in determining the stage and prognosis of cancer, and its treatment often involves targeted therapies and interventions aimed at controlling or eradicating the metastatic cancer cells.