Yes, you are incorrect in the context of this article. You should read it.

One of the theories is that for whales, they are so large their cancer gets cancer and dies before the cancer is large enough to effect them. Or genes prevent them from getting it, etc.

There are a number of ways that whales are different from humans, and there is no reason that the cancer scaling with mass in humans is invalidated by whales.

Human men are pretty similar to human women, whales are kind of different. So the number of cells alone is quite a good way to differentiate men and women, not so much humans and whales.

Humans have a "tumour suppressor gene" called p53 which helps reduce the occurrence of cancers. Elephants (not quite whale size, but still pretty big!) have been shown to simultaneously express 20 variants of p53 which is thought to (at least partially) account for the lack of an expected increase in incidences of tumours given their sheer number of cells.

Further reading: http://www.nature.com/news/how-elephants-avoid-cancer-1.1853...