The use of vitamin C in alternative cancer treatment isn't new. Proponents claim that large doses of vitamin C are toxic to cancer cells. However, there is no reliable evidence gathered in human studies to support this theory.
Studies in the 1970s first suggested that large doses of supplemental vitamin C might be of some benefit in the treatment of cancer. But these studies were later found to have serious flaws. Subsequent well-designed, randomized, controlled trials of vitamin C and cancer found no such treatment benefit.
More recently, vitamin C given intravenously (IV) has been touted to have different effects than vitamin C taken orally. This has prompted renewed interest in the use of IV vitamin C as a cancer therapy. However, there is still no evidence that vitamin C has any effect on cancer. Until clinical trials are completed, it's premature to determine what role, if any, IV vitamin C may play in the treatment of cancer.