Cancer of the prostate: a nutritional disease?

UNLABELLED

In summary, epidemiologic and laboratory evidence increasingly demonstrate that nutritional factors, especially reduced fat intake, soy proteins, vitamin E derivatives, and selenium, may have a protective effect against prostate cancer. The experimental observation that low-fat diets and soy protein extracts may influence the progression of established tumors, rather than inhibiting etiologic factors, is particularly intriguing because it may serve to help explain the paradox whereby the incidence of clinical prostate cancer shows wide geographic variation, yet the evidence persists that the incidence of microfocal tumors is essentially the same worldwide. These observations, plus the likelihood that nutrition trials are likely to have little in the way of toxicity that would preclude their completion, argue that such trials should be performed. It is estimated that 30% to 50% of human malignancies may be related to dietary factors, and although the feasibility of trials involving low-fat diets has been proved in ongoing trials for colon and breast cancer, no similar study exists for prostate malignancy. Critics of epidemiologic research argue that data derived from case-control studies are subject to recall bias and are thus artifactual. Indeed, many researchers now believe that the breast cancer-dietary fat hypothesis has been discredited. The major difference between the prostate cancer and breast cancer literature is the remarkable consistency of the cohort studies. In these studies, exposure is determined prospectively and is therefore free from recall bias. In this sense they more closely resemble a clinical trial. The majority of cohort studies involving dietary fat and breast cancer have been negative. We believe that these data justify large-scale trials in the area of prevention of prostate cancer. One such proposed study already submitted for National Institutes of Health funding from a consortium of centers is the Prostate Interventional Nutrition Study (PINS), modeled after the Women's Interventional Nutrition Study, which investigates the effect of low-fat diets in women receiving therapy for node-positive breast cancer. The PINS study will be limited to men who have detectable serum PSA levels but no other clinical evidence of disease after radical prostatectomy. All subjects will receive nutritional guidance, with randomization between a control arm receiving the currently recommended 30% fat diet and an interventional arm in which a 15% fat diet is supplemented with soy protein, vitamin E, and selenium. The end points for evaluation will be compared with progression based on changes in PSA and the time of onset of clinical, as opposed to biochemical, disease. Single-institution trials involving groups thought to be at high risk of developing clinical cancer--including men with persistently elevated PSA levels, two negative prostate biopsies, high-grade prostatic intraepithelial neoplasia on biopsy, and a strong family history of prostate cancer--are being initiated at MSKCC and other institutions.

CONCLUSIONS

We have reviewed the evidence that nutritional factors play a role in the progression rate of prostate cancer and may help to explain the geographic variation in the incidence observed. However, without well-controlled prospective trials, the attractive hypothesis that nutrition plays a role in tumor progression remains simply an attractive hypothesis. To date, no definite proof of a preventive effect has been shown in a study that will withstand rigid scientific scrutiny. The opportunity exists, however, for the urologic community, working together with experts in the area of nutrition, not only to advance our understanding of prostate tumorigenesis, but to rebut those critics of modern medical technology who claim that we have ignored the total or holistic approach to healing. (ABSTRACT TRUNCATED)