[discostu]

Probably because their owners take them to the vet more often and subsequently they live longer. Cancer is the little expiration date God put on all His creatures, the longer you live the more likely it is you'll die of cancer.

[webstersII]

"Cancer is the little
expiration date God put on all His creatures"

Umm, I don't think so.

Cancer is a mutation of host cells, not a way for an organism to do a pre-planned expiration. The pre-planned expiration is already part of the cell process; it's why people age normally.