Question of whether vitamin E prevents or promotes cancer has been widely debated in scientific journals and in the news media. Recently the research conducted by the scientists at Rutgers seems answer the question.
They believe that two forms of vitamin E, natural forms found in food and the high-dose synthetic E in most supplements, have different effect. The natural forms may lower cancer risk while the synthetic E may actually cancels the benefit of the good vitamin E from food and perhaps increasing the odds to get cancer.
So I guess we probably should rely on foods such as vegetable oil and nuts, not too much on the supplement.
More detail info can be found here: http://news.rutgers.edu/medrel/news-releases/2012/04/rutgers-study-vitami-20120420