Experimental studies suggest that both quantity and quality of dietary lipid can influence the developmental course of several major forms of cancer -- notably skin, mammae, and intestine. For some cancers, epidemiological data support these studies and demonstrate a positive correlation between dietary fat intake and mortality rates. It is ironic, however, that the relationship of diet to skin cancer, both of which manifest lifestyle, has received so little attention. The specific aim of this proposal then is to determine, in a close- controlled clinical setting, whether dietary modification of lipid intake can alter the course of skin cancer development. 700 patients presenting with a reference skin carcinoma will undergo a series of laboratory and dietary base-line evaluations. Upon qualification, the 700 patients will be randomized into two groups of 350 each. One group will be a Non-Intervention (NI) group in which no changes in dietary habits will be initiated and from which the control rate of carcinoma occurrence will be derived. The remaining group (Dietary Intervention, DI), will adopt a diet characterized by reduced fat intake (20% of total caloric intake). Both groups will be examined at 4 month intervals, over 24 months, for carcinoma incidence. In addition, the DI group will be evaluated monthly for dietary compliance and reinforced with respect to dietary goals. Laboratory tests will be completed at designated intervals to monitor dietary compliance and to detect any adverse side- effects of he low-fat diet. This intervention design will allow a direct comparison of dietary lipid exposure levels and disease status. If low fat DI effects tumor progression along the carcinogenic continuum as expected than a reduced incidence of subsequent carcinomas will occur in the 24 month follow-up when the normal occurrence approaches 30%. In toto, this study will not only avail a potential means for prevention and/or management of a common malignancy, but will provide direct and definitive evidence for the involvement of dietary lipids in carcinogenesis, with implications for other forms of cancer as well.