How likely is it that cancer is evolution gone wrong?

It IS: In fact, natural selection -- which drives darwinian evolution in the emergent natural world -- also causes cancers to accumulate genes for irresponsible growth. The ability to the genes to mutate, which is necessary for evolution on earth, also makes cancer inevitable in individuals as they age if someting else does not kill first. You have a deep insight. Best wishes.

It is not: The process of evolution is the nonrandom selection of random genetic changes. Evolution cannot "go wrong." A young cancer death before reproducing removes the mutation thus strengthening the "herd;" a cancer death after reproducing weakens the herd & selects for other, "stronger" herds. DNA replication may "go wrong," but evolution does not.