Epidemiological studies have indicated that whole-grain intake has a protective effect against cancer. Our previous report showed that brown rice extracts have cytotoxic effects on hormone-dependent and -independent breast cancer cells. The present study was carried out to investigate anticarcinogenic potential of dietary brown rice in experimental rat mammary carcinogenesis. At 52 days of age, female Sprague-Dawley rats were given a single dose of 5mg 7,12-dimethylbenz-(a)anthracene (DMBA) by an intragastric administration. Animals were subdivided into 4 groups with 10 animals each and fed experimental diets for 23 weeks. Diets were composed as follows: AIN-76 control diet (CT), AIN-76 control diet⁢50% brown rice (CTBR), AIN-76 control diet with 20% corn oil (HF), AIN-76 control diet with 20% corn oil ⁢ 50% brown rice (HFBR). Beginning 8 wks after DMBA administration, all rats were palpated weekly for mammary tumors, and the tumor incidence, location, and size were recorded for fuerhwe 15 wks. Results indicted that brown rice tended to decrease tumor size in rats fed either control diet or high fat diet. Breast tumor incidence, 20% in CTBR, 22% in CT, 33% in HFBR, 44% in HF. HF-fed animals had the shortest latency period and brown rice diet delayed the period, although no statistical significance was found. It is concluded that brown rice-based diet may suppress the formation of mammary tumors and tumor growth, however, further studies are required to elucidate possible mechanisms and responsible compound(s).

Keywords: Whole grain, Brown rice, Breast cancer, DMBA