metastasize

The word metastasize comes from Greek and carries the idea of changing place. That is what happens when cancer cells leave the part of the body where they first appeared and travel somewhere else, often through the blood or the lymphatic system. When they settle in a new organ or tissue and begin growing there, they form new tumors. This process is called metastasis.

It is important to see the difference between growth and spread. A tumor can become larger without metastasizing. But if it metastasizes, cancer cells have broken away from the primary tumor, traveled to another place, and started to grow there. For example, breast cancer may metastasize to the lungs, liver, or bones.

Doctors watch closely for signs of metastasis because it can strongly affect treatment choices and the likely outcome. If cancer has metastasized, treatment often becomes more difficult because the disease is no longer limited to one place. Although the word is mainly used in medicine, it is also sometimes used in a figurative way to describe something harmful spreading and becoming harder to control, as in "violence metastasizing throughout a region" or "corruption metastasizing within a government."

In short, simple growth means getting bigger in one place, while to metastasize means spreading to new places and turning one local disease into a wider problem.