Respiratory tract carcinogenesis in hamsters induced by different numbers of administrations of benzo(a)pyrene and ferric oxide.

Benzo(a)pyrene (BP), prepared as a suspension of fine crystalline particles attached to particles of ferric oxide in 0.9% NaCl solution, was administered by intratracheal instillation to Syrian golden hamsters. A single administration of 37.5 mg BP with 12.5 mg ferric oxide in 0.5 ml 0.9% NaCl solution induced five bronchogenic carcinomas and five histologically benign respiratory tumors in a total of 61 hamsters. A single administration of 5 mg BP with 45 mg ferric oxide in 0.5 ml 0.9% NaCl solution induced one peripheral adenocarcinoma and six histologically benign respiratory tumors in a total of 189 hamsters. Repeated instillations, each of 3 mg BP with 3 mg ferric oxide in 0.20 ml 0.9% NaCl solution, were administered 5,10, or 15 times; two experimental groups were used at each dose level. Respiratory tract tumors, mostly bronchogenic carcinomas, were induced in all groups, and a positive dose-response relationship was demonstrated.