Spontaneous tumor incidence in female brown Norway rats after lifelong diets high and low in linoleic acid.

High linoleic acid (C18:2) (group I; 17.7 cal%) and low C18:2 (group II; 3.3 cal%) diets were given to groups of inbred Brown Norway virgin female rats (100 animals/group), during their whole life-span. A total of 140 tumors were found in group I and 123 tumors in group II; the median survival times of the 2 groups were 124.2 and 118.5 weeks, respectively. Total spontaneous tumor incidence and median survival times were not significantly different. However, significant differences were found in the incidences of some specific tumors: The numbers of reticuloendothelial tumors and adrenocortical carcinomas were significantly higher in the group of animals receiving the low-C18:2 diet. A high incidence of tumor multiplicity, however, resulted in a significantly greater number of mammary tumors in the high-C18:2 diet group.