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Importance of physical properties of benzo(a)pyrene-ferric oxide mixtures in lung tumor induction.

Three mixtures of benzo(alpha)(a)pyrene (BP) and ferric oxide with different physical properties were given intratracheally to Syrian golden hamsters for an examination of their neoplastic potential. Hamsters treated with a preparation containing large aggregates of BP and ferric oxide resulting from nucleation of BP on the particles showed an earlier onset and higher incidence of respiratory tract tumors than animals given a mixture containing smaller aggregates prepared by hand-grinding. The greatest number of tumors were present in the trachea and the predominant type was the squamous carcinoma. A third preparation in which the carcinogen was not attached to the ferric oxide showed a low tumor incidence similar to that present after intratracheal intubation of BP in gelatin without a carrier particle. For this model system of respiratory carcinogenesis, the physical attachment of BP and the carrier dust is necessary for a high tumor yield.