I don't quite follow that logic. Cancerous cells are genetically different from normal ones. I think it is fairly widely held that cancer is caused from genetic mutations to healthy cells. Otherwise we'd be built from cancer.

But those cancer cells probably come from genetic damage in the environment in most cases. Or a combination of a genetic propensity AND environmental triggers. Maybe some cancers are purely due to genes. There are some cancers that are due to viruses and other diseases.