Abstract PR-1: A randomized factorial trial of vitamins E and C in the prevention of cancer in men: the Physicians' Health Study II

Abstract

Abstract PR-1 Background Basic science and observational studies support a potential role of antioxidants, including vitamins E and C, in the prevention of cancer. Previous trials have suggested a possible benefit of vitamin E, in particular on prostate cancer. Few long-term trials have evaluated vitamin C alone in the prevention of cancer. Despite uncertainty regarding long-term effects, use of vitamin supplementation remains highly prevalent in the US. Methods The Physicians’ Health Study II (PHS II) evaluated the roles of supplementation with vitamin E (400 IU every other day) and vitamin C (500 mg daily) on risk of cancer in a randomized, double-blind, placebo-controlled trial of 14,641 U.S. male physicians initially aged ≥50 years. The trial included 1,274 (8.7%) men with prevalent cancer at randomization. The randomized vitamin E and C trial components terminated as scheduled on August 31, 2007, and identification of cancer endpoints that occurred prior to that date will continue through September 30, 2008. The primary endpoint of the vitamin E component was prostate cancer, with total cancer (defined as excluding non-melanoma skin cancer) as a secondary endpoint. For vitamin C, the primary endpoint was total cancer. All endpoints were reviewed and confirmed by an Endpoints Committee of physicians blinded to randomized treatment assignment. High rates of morbidity and mortality follow-up have been maintained in the PHS II. Results During a median (interquartile range) follow-up of 7.6 (7.1 to 9.6) years among men with a mean baseline age of 64.3 years, there have been 1,929 cases of cancer, including 1,013 cases of prostate cancer. Based upon preliminary results, those randomized to vitamin E had a relative risk of prostate cancer of 0.95 (490 events in the active group vs. 523 in the placebo group; 95% CI, 0.84-1.07; p=0.39), and a relative risk of total cancer of 1.04 (978 vs 951; 95% confidence interval, 0.95-1.14; p=0.38). For those randomized to vitamin C, the relative risk of total cancer was 1.00 (964 events in the active group, 965 in placebo; 95% CI, 0.92-1.10; p=0.95). In addition to updating the results above, we will also present the results for other site-specific cancers, as well as analyses that consider the effects of compliance, effect modification by baseline risk factors and baseline cancer, and potential adverse effects. Conclusion These preliminary data from a large-scale prevention trial of long duration indicate no beneficial effect of vitamin E supplementation on either prostate or total cancer, nor a beneficial effect of vitamin C supplementation on total cancer. These data will help inform clinical and public health recommendations regarding effects of vitamin E or vitamin C supplementation on risks of total and site-specific cancers. Citation Information: Cancer Prev Res 2008;1(7 Suppl):PR-1.