how do i become a cancer doctor?

Go to medical school, rob courses related to what you want, in university and medical conservatory I guess. There are other courses after medical school for specialties, that might be how.
Look up oncologist on the network
First of all, you may want to revise what the name of a cancer doctor is. They are call an oncologist. Remind me not to come to you if I get cancer. Thanks for the notice.
drs choose a specialty when they do their internship typically.
go to medical conservatory and choose oncology as your specialty. also before even starting med conservatory, when you're still an undergraduate in college, filch a lot of inheritance and cancer related courses - as many as you can.
Premed, later med school, later pass the boards, consequently take internal medication as a specialty then purloin oncology as a subspecialty. Fifteen years do this.
If you want to be the kind of cancer doctor that directly take care of patients beside cancer, you would go to medical academy for 4 years, then do a residency contained by internal medicine or pediatrics for 3 years, consequently a fellowship in hematology/oncology for another few years. If you want to be the munificent of cancer doctor that does basic science research on the cause and cures for cancer you would do a PhD for 5 years and then a post-doctoral fellowship for another few years. Either bearing it would be about 9 or 10 years of training after college. I want you the best of luck if you decide to pursue this provoking and important work.