Diet and anticarcinogenesis in the mouse skin two-stage model.

The initiation-promotion model for the production of skin tumors in mice has proven useful for studying the influence of nutritional variations on stages in neoplasia. Specifically, restriction in caloric intake or fat level in the diet as well as a supplemental retinoid protect against tumor promotion. In contrast, the level of calories and fat ingested as well as supplemental retinoids are without effect on initiation. Elevated levels of ornithine decarboxylase activity is one of the essential components of the mechanism of neoplasia. The assay of a dietary constituent for its ability to depress the level of the enzyme in a target tissue and particularly to inhibit the induction of the enzyme in mouse epidermis by the tumor-promoting phorbol ester may be indicative of the ability of that constituent to protect against neoplasia.