EFFECTS OF TYPE AND AMOUNT OF DIETARY-FAT ON MOUSE SKIN TUMOR PROMOTION

In a previous study (Cancer Res 51, 907, 1991) in which we found an in verse relationship between quantity of dietary) corn oil and saturated fat, in a constant 15% fat diet, on the tumor promotion stage of skin carcinogenesis, it was not clear whether one or both types of fat pla yed a modulatory role. The purpose of the present study therefore was to compare the effect of 1) increasing corn oil in corn oil-only diets and 2) increasing saturated fat, with a constant level of 5% corn oil , on tumor promotion. In the first study, the effects of five levels o f dietary corn oil (5%, 10%, 15%, 20%, and 25%) on the incidence and r ate of papilloma and carcinoma development were determined in female S encar mice fed these diets one week after initiation with 7,12-dimethy lbenz[a]anthracene and three weeks before the start of promotion with 12-O-tetradecanoylphorbol-13-acetate. A papilloma incidence,of 100% wa s reached first in the 5% corn oil group, at 10 weeks, followed by the 10% group al 13 weeks and the 15% and 20% group at 16 weeks. The high est corn oil group achieved a 90% incidence. There were marked differe nces in latency of carcinoma development among the diet groups. At Wee k 29, the curmulative carcinoma incidence was 56% and 32% respectivel) , in the 5% and 10% corn oil groups, whereas the incidence in the two highest corn oil (20% and 25%) groups was only 8% and 4%, respectively . In the second study, the effects of diets containing 5% corn oil and increasing levels of coconut oil (5%, 10%, 15%, and 20%) on the incid ence and rate of papilloma and carcinoma development were determined, as described above. No significant difference in latency or incidence of papillomas or carcinomas was noted among these saturated fat diet g roups. It thus appears thar higher levels of dietary corn oil are asso ciated with a reduced cancer incidence in this model system.