Is metastasis a behaviour?

Chris - Indeed it is, because what's happening when a cancer spreads is that the cancer is spitting off cells that have gained the ability to autonomously migrate through other tissue layers, ignoring normal boundaries, to move to a distant part of the body. They then move into that part of the body where other cells, which are not cancerous but are healthy tissue, have been manipulated by chemicals produced by the cancer to flock to that area, and produce - for all intents and purposes - a nest for that cancer cell to move in to, and then begin to grow. Then you develop another secondary cancer and that's the metastasis. It's a complicated process that scientists are only just beginning to understand.