In what ways are cancer patients able to hide their illness so well?

Cancer is internal: Many times with the cancers, there are no external stigmata. Also, many of the treatments are much better tolerated than previously. The chemotherapeutic agents are more specific and more targeted, thus many of the bad side effects are decreased. Thus, the old image of sickly, infirm , bedridden patients may be less prevalent. Obviously, this is on a case by case basis.