One of the take-home messages from this documentary is that cancer is not a single disease. It is a cluster of 200 diseases, since there are about 200 cell types in the human body. http://www.pbs.org/show/story-cancer-emperor-all-maladies/
There's also the microbiome effects, which people only thought to look for recently. https://www.theatlantic.com/science/archive/2017/09/how-bacteria-could-protect-tumors-from-anticancer-drugs/539670/
It's not only the different cell groups that can evolve into different types of cancer. Each cell is capable of mutating into cancer due to different sets of changes in their genome. Theoretically there's an infinite number of cancers, though most of the time we only see the more common variants.
For example basal cell carcinoma and squamous cell carcinomas (two of the most common skin tumours) both arise from a single cells type, during different stages of it's development. The same can be said for all the types of lymphoma and a number of the luekemias which have a large amount of practical overlap.