It means to spread, as in a diseased tumor as it spreads to other parts of the body. So if someone had cancer of the stomach, it could spread (metastisize) to the lungs and start growing there as well as the stomach.
Do a search for the effects of Lung Cancer. The original source (Thyroid) is immaterial.
Metastasis is a common word used when referring to cancer. If something is said to have metastisized it means that it is on the move in the body, moving from location to location. This causes the tumor, clot, or cancer to be able to spread throughout the body, thus effecting more of the body and killing is sooner.
It had spread too much. Trying to remove as many as possible would have made her life even harder and she could've gotten infections on top of still having cancer. They could not remove them all..
Well, darling, here's the tea: heart cancer is as rare as a unicorn sighting, so there isn't a specific survival rate for it. Most heart-related issues are due to other factors like heart disease or failure. So, if you're worried about heart cancer, you can rest easy knowing it's about as common as finding a leprechaun's pot of gold at the end of a rainbow.