Combination effects of forty carcinogens administered at low doses to male rats.

An investigation was conducted to determine whether a mixture of low doses of forty carcinogens that target different organs, including the liver, intestine, thyroid, urinary bladder, and skin, is effective for tumor induction in F344/DuCrj rats. The dose of each carcinogen in the diet was 1/50 of the TD50 value, treatment being continued for 102 weeks. Significant numbers of neoplastic nodules of the liver and follicular cell tumors of the thyroid developed in the animals exposed to the carcinogen mixture, although the question of whether the observed carcinogenic effects were synergistic or additive could not be answered. The results serve to evaluate carcinogenic risk in the search for causes of human cancer.