Mammary tumorigenesis in rats fed diets high in lard

Studies were performed to examine the effect of a lard diet on tumorigenesis by 7,12-dimethylbenzanthracene (DMBA), given parenterally rather than by gavage, to eliminate any effect of the high lard diet on carcinogen absorption. In addition, the effect of low dietary levels of the antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in the tumor model was evaluated. The lards fed were analyzed for fatty acid composition and content of certain potential contaminants. DMBA induced tumors when given by intravenous or subcutaneous injection. The high lard diet appeared to enhance tumorigenesis in rats given a dose of 0.25 mg (10% of the gavage dose) by injection into the mammary gland, although the effect was not statistically significant. In other experiments using lard from different sources and DMBA given by gavage, significant enhancement of tumorigenesis was limited to groups fed the high lard diets throughout the experiment or beginning after DMBA exposure. In contrast to earlier results, there was no demonstrable effect of feeding the high lard diets before DMBA administration. Addition of BHA and BHT to the lard at the concentration assayed in commercial lard samples or at the maximum concentration permitted did not influence the tumorigenesis. In groups in which tumorigenesis was enhanced by the high lard diet, the incidence of malignant, invasive tumors was higher than in other groups.