Obviously, that whales are much larger than people are, which means that their bodies have the more cells. And every cell in the body can theoretically become malignant. Consequently, the whale is much more likely to develop cancer than people, right?
This is not quite accurate. Peto's Paradox, named after Professor of Oxford Richard Peto, argues that the correlation between the size of the animal and the cancer does not exist. Humans and whales have the same chance of getting cancer, but some breeds of tiny mice have much more chances.
Some biologists believe that the lack of correlation in Peto's paradox can be explained by the fact that the larger animals are more resistant tumor: the mechanism works in such a way as to prevent the mutation of cells during division.