I would argue that cancer is more of a consequence of aging, genetics, and environmental factors and not a "feature". Cells have evolved multiple mechanisms to prevent rampant and uncontrolled growth. With cancer these mechanisms are perturbed through genetic alterations due to "bad luck" or the consequences I mentioned previously.
You can also think of cancer as a consequence of multicellularity.
Multicellular organisms need checks on how often and by how much a group of their cells can multiply. A liver must contain a specific amount of liver cells, and cancer occurs when these cells are able to continually divide and eventually activate non liver specific genes.
The cells of a multicellular organism become highly altruistic because each cell of the organism gives up its ability to reproduce in order to provide a chance for the organism's gametes to produce a new living organism.
So wyldfire's original comment on Cancer being a 'feature' is not necessarily incorrect, however the explanation is.
Cancer occurs when the contract that states that the Liver cells, who cannot reproduce, become able to continually divide without checks and balances. You can also almost think of Cancer as Cellular natural selection and evolution within the body. Cancer is a feature and consequence of multicellularity and likely not adaptive in any way such as sickle cell anemia and malaria resistance.
