Vitamin C and cancer: what can we conclude--1,609 patients and 33 years later?

In 1976 an article co-authored by Linus Pauling described that 100 terminal cancer patients treated with intravenous vitamin C, followed by oral maintenance, lived four times longer than a control group of 1,000 patients who did not receive vitamin C. The study was strongly criticized because the control group was very different from the group treated with vitamin C. The latter were declared terminally ill much sooner than the control group thus resulting in an artificially longer survival for the vitamin C group. Three double blind placebo controlled randomized trials performed at Mayo Clinic using oral vitamin C for cancer patients were negative. In a phase I-II trial performed by Riordan et al, none of 24 cancer patients treated with i.v. vitamin C responded. At this point we don't have information as to which is the actual plasma level of vitamin C that can produce tumor shrinkage. We don't have consistent information either regarding what is the clinical dose necessary to yield therapeutic plasma levels. In view of this lack of data after trials which have included at least 1,591 patients over 33 years, we have to conclude that we still do not know whether Vitamin C has any clinically significant antitumor activity. Nor do we know which histological types of cancers, if any, are susceptible to this agent. Finally, we don't know what the recommended dose of Vitamin C is, if there is indeed such a dose, that can produce an anti-tumor response.