According to a long-term study, Vitamin C and E supplements do not prevent cancer, at least not in the large group of doctors studied.
I haven’t taken the vitamin E supplements used in this study for awhile, because of some negative studies associated with it. Apparently, the worst form is dl-alpha tocopherol, the synthetic form, which is what the study referenced above used. 400 IU seems to be too much too. I take 200 IU occasionally, but it is the all natural form of vitamin E, with mixed tocopherols. I wonder how Vitamin C would have fared individually, without being accompanied by a high dose of Vitamin E.