Inhibition of Tumor Growth in Rats by Feeding a Polychlorinated Biphenyl, Aroclor 1254 Nancy Isaacson Kerkvliet Donald J. Kimeldorf Department ef Veterinary Medicine Department of General Science Oregon State University Oregon State University Corvallis, Ore. 97331 Corvaflis, Ore. 97381 Polychlorinated biphenyls (PCBs) are globally distributed, highly persistent environmental contamin- ants (RISEBROUGH et. al. 1968, PEAKALL and LINCER 1970). Several adverse toxicological effects have been attributed to PCB exposure, including a potential hepa- tocarcinogenicity (ITO et~ al. 1973, ITO et. al. 1974, KIMBROUGH and LINDER 1974). PCBs have also been re- ported to act as irmmunosuppressive agents (VOS and BEEMS 1971, VOS and DE ROIJ 1972, KOLLER and THIGPEN 1973). Since a suppressed immunologic state in the host can enhance the generation and growth of tumors (BURNET 1970, GATTI and GOOD 1971, PENN and STARZL 1972, HERBERMAN 1974), we conducted the following study to determine the effects of host exposure to PCBs on tumor growth per s_ee, utilizing a transplantable tumor in rats. MATERIALS AND METHODS Aroclor 12541, dissolved in corn oil, was incorp- orated into specially prepared powdered diets at levels of 0, i00, 400 or 800 ppm and fed to groups of male and female Sprague Dawley rats, eight of each sex per group. Subsequently, three additional groups of 20 male rats were placed on diets containing 0, 5 or 25 ppm PCB. All animals were approximately one month of age at the start of the experiment. Food consumption was measured three times per week for each animal and body weights were re- corded weekly. Following 30 days of exposure to the contaminanted diets, the animals were inoculated with the Walker 256 carcinosarcoma in the flexor muscle mass of each hind limb. Each injection consisted of 1 x 105 Walker tumor cells (obtained from the ascites form of the tumor) in a volume of 0.i ml. The tumors were allowed to grow for nine days, during which time the animals remained on their respective diets. At sacrifice, the animals were killed by ether asphyxiation and the tumors were re- moved, dissected free of surrounding connective tissue 1 Monsanto Chemical Co., St. Louis, Missouri 243 Bulletin of Environmental Contamination & Toxicology, Vol. 18, No, 2 9 1977 by Springer-Verlag New York Inc.