Experimental Respiratory Carcinogenesis in Hamsters: Environmental, Physicochemical and Biological Aspects

Abstract

The respiratory tract of Syrian golden hamsters was exposed to polycyclic hydrocarbons alone and in combination with dusts. These included benzo(a)pyrene (B(a)P), silicon dioxide (SiO₂), manganese dioxide (MnO₂) and agar gelatin (gel), as well as dibenz(a, j)acridine (DBA) in combination with the carrier dust ferric oxide (Fe₂O₃). The purpose of the study was to evaluate the possible environmental hazards of these compounds and the physicochemical characteristics determining their carcinogenic activity. We also wished to study the prognostic significance of premalignant alterations in relation to treatment by carcinogenic and noncarcinogenic agents and the applicability of respiratory tumor classification in this system. When instilled alone, the dusts induced bronchial nonspecific epithelial alterations, interstitial cell proliferation and a few granulomatous changes in the lung. No respiratory tract tumors were seen. B(a)P alone induced only tracheal epithelial alterations, desquamation and metaplasia, as well as five papillomas and one squamous cell carcinoma. B(a)P in a suspension of gelatin-saline induced a few papillomas and squamous cell carcinomas of the trachea and lungs. SiO₂ with B(a)P was highly effective and induced papillomas, squamous cell carcinomas, adenomas and adenocarcinomas of the larynx, trachea and lungs. They were preceded by epithelial proliferative dysplastic alterations, not seen in animals treated with B(a)P and MnO₂ or DBA and Fe₂O₃. These groups also failed to exhibit a significant neoplastic response. The tumors could be divided into benign and malignant, glandular or squamous cell tumors. The trachea, main bronchi, bronchioli and lungs showed the efficacy and applicability of a classification similar to that used in man. It is also concluded that preneoplastic alterations sufficient in degree and extent are indicative of subsequent tumor formation.