Dietary fat and breast cancer risk: the feasibility of a clinical trial of breast cancer prevention.

Animal experimental evidence and human ecological data suggest that dietary fat intake is related to breast cancer risk. Epidemiological studies within countries have given inconsistent results but are limited by the restricted range of dietary intake found in Western populations and by error in the measurement of fat consumption. Experimental evidence, derived from controlled clinical trials in which the range of fat intake is increased beyond that seen in most Western populations, is capable of overcoming this limitation of observational epidemiology, and would provide the strongest evidence available concerning the relationship of dietary fat intake to breast cancer risk. Further, such trials are the only means likely to answer the question of whether breast cancer risk in high-risk subjects can be modified by changing dietary fat intake. We describe here several aspects of the feasibility of an experimental approach to this problem, including the identification of subjects at increased risk for breast cancer, and the demonstration that such subjects will enter a clinical trial of dietary fat reduction and comply with a low-fat diet. It is shown that subjects can be recruited and retained in such trials, that satisfactory dietary compliance can be achieved over at least 24 mon and that the subjects selected are at demonstrably increased risk of breast cancer. This finding indicates that it is feasible to test the dietary fat-breast cancer hypothesis experimentally by means of a clinical trial.