FAILURE OF HIGH-FAT DIETS TO PROMOTE MAMMARY CANCERS IN SPONTANEOUSLY HYPERTENSIVE RATS

Rat strains differ in their susceptibilities to chemically-induced mammary carcinogenesis. The present study tested the hypothesis that the spontaneously hypertensive rat (SHR) strain is resistant to mammary carcinogenesis. Resistance would imply the presence of the mammary carcinoma suppressor (MCS) gene. Therefore, we also wanted to test the ability of this gene to inhibit mammary tumor promotion in the presence of high fat diets. Female SHRs were treated with DMBA (5 mg/rat) at 50 days of age and transferred to either a 20% corn oil or 19% menhaden oil + 1% corn oil diet one week later. At 17 weeks post-DMBA none of the rats in either group developed mammary carcinomas. Multiple palpable nodules formed in the mammary gland indicating that initiation had occurred. We conclude that the SHR strain is genetically resistant to DMBA-induced mammary carcinogenesis by mechanisms involving a blockade of promotion.