Other forms: metastases
When a doctor uses the word metastasis, it's never good news. It means an illness has spread to new parts of the body.
The noun metastasis is a medical term that's most often used to describe a spreading cancer. If a patient's lung cancer spreads to his heart or to his lymph nodes, that is metastasis. It's a Greek word meaning "transference or change." In Latin, the word metastasis was at one time used to mean "a sudden transition in subjects," but ever since the 1660s, the English use has been almost entirely medical.