"marketing and advertising" also means informing doctors about new drugs and therapies. Outside of "miracle" drugs or new drug categories (e.g. ED or the low side effecting SSRIs like Prozac) that get "promoted" by the media etc. a new drug will do few any good if doctors don't know enough about it.
This is especially true for cancer drugs marketed to oncologists (which I suspect are never marketed directly to consumers...). The field is very complex ... and I recall that one of the major factors in the difference in outcomes between your local medical system and the major cancer centers is the better current knowledge of the practitioners in the latter.
Even though some drugs are indeed more lucrative for them than others, they would not develop cancer drugs if they were not profitable.