http://www.sciencedaily.com/releases/2007/02/070218194439.htm
"When cells become cancerous, they also become 100 times more likely to genetically mutate than regular cells, researchers have found. The findings may explain why cells in a tumor have so many genetic mutations, but could also be bad news for cancer treatments that target a particular gene controlling cancer malignancy."
http://www.sciencedaily.com/releases/2007/02/070218194439.htm
Many things mutate. Cancerous cells are one of them.
Yes, cancerous cells mutate. No, they do not mutate to adapt.
They are mutations of normal cells, they mutate so much because they split so rapidly, forming the cancerous tumor. There is no adaptation, mutations are just a side effect of the cancer.
Cancer is effectively broken cells that don't die and don't stop reproducing. It's not a virus that you can kill only to have it adapt and come back stronger.
I see where you both went wrong over my statement though.