well, about how does the the cancer cells may evolve maybe u can consider it from the most important structure of cell itself_ the DNA. i had come across fews articles before which state that cancer can be inherited (correct me if this is wrong). After many extensive study were done, the similar potential DNA sequence that cause several types of cancers were found in some of the patients with similar diseases or in other words, it is encoded in our DNA as long as our DNA repair mechanisms cannot detect the defective region. so imo, since few groups of cells are different from the other, different type of cancer may arise in different individual but of course, not everyone with the defective DNA will get the disease. some other factors are crucial too. from your post, i agree that although these cells are functioning normally at first but until at a certain period, there is external trigger which disrupt their process or else, it is sure to occur but it just a matter of time.
