Many cancer survivors become very interested in health issues. It is important to consider the benefits and harms of complementary and alternative therapies, before starting any new therapies. Generally there is little or no evidence to suggest that alternative therapies will help prevent recurrence or secondary cancers.
Scientific research is investigating if taking vitamin supplements helps cancer survivors. The results so far have not supported the use of vitamins at doses above the recommended dietary intake.
We do know that eating vegetables and fruits may reduce the risk of some cancers. Vegetables and fruits contain a variety of vitamins, minerals and protective substances (like phytochemicals). We are only just beginning to discover the many beneficial plant substances that exist. A tablet cannot possibly replace the real thing.
As a general rule, dietary supplements should never replace whole foods.