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.