Co-carcinogenic effect of chrysotile and amosite asbestos with benzo(a)pyrene in the lung of hamsters.

To clarify co-carcinogenic effects of chrysotile (Chry) and amosite (Amo) asbestos with benzo(a)pyrene (Bap), 0.2 mg UICC (International Union against Cancer) standard reference sample of asbestos and 0.4 mg Bap were applied intratracheally once a week for 6 weeks. Eighteen and 24 months after the last instillation the number of tumors was examined. The Chry + Bap group yielded 37 tumors including 16 carcinomas in 12 animals, and the Amo + Bap group yielded 30 tumors including 11 carcinomas in 12 animals. Tumor-bearing animals were 100% in the Chry + Bap group and 92% in the Amo + Bap group, and carcinoma-bearing animals were 83% and 67%, respectively. The animals injected with Chry, Amo, and Bap alone developed no tumors. The number of tumors and carcinomas and the frequency of the tumor- or carcinoma-bearing animals in Chry + Bap and Amo + Bap were significantly higher than those of the groups injected independently. The number of tumors or the frequency of tumor-bearing animals was higher in Chry + Bap than in Amo + Bap; however, these differences were not significant. These results indicate that both Chry and Amo play an important role in the genesis of bronchogenic carcinoma.