Co-carcinogenic effect of asbestos and benzo(a)pyrene in the lung of hamster

Epidemiological reports indicate that occupational asbestos exposure and smoking habit make increase the incidence of lung carcinomas greatly. To elucidate the synergetic effect of smoking and asbestos exposure, hamsters were injected intratracheally with asbestos and benzo(a)pyrene(Bap), which is contained in cigarette smoke, singly or in combination. Tumor was not induced in the hamsters injected with asbestos or Bap alone except epithelial hyperplasia. On the other hand, 7 tumors out of 34 animals were found in groups injected with both asbestos and Bap from 12 months to 19 months after injection. Two of them were carcinomas. This result seemed to indicate synergetic effect of asbestos and Bap in causing carcinoma of the lung.