Induction of lung tumors by radioactive isotopes implanted in the rat lung.

Squamous cell carcinomas were induced in the lungs of male WAG/Rij inbred rats by radiation emitted from the isotopes iridium-192 or iodine-125. These isotopes were implanted by a surgical procedure in the lungs of young rats. Forty rats received implants of 192Ir wires and 20 animals, of 125I seeds. In a 14-month observation period, 30 of the 40 animals with implants of 192Ir wires developed tumors. Malignant hemangioendotheliomas occurred with the highest frequency (50%). From the lungs of 12 rats, squamous cell carcinomas were found. In the observation period of 17 months, 3 rats with implants of 125I seeds developed tumors, among which 1 squamous cell carcinoma could be identified. Tumor fragments were transplanted in syngeneic hosts for propagation of the tumors. Histologic appearances of tumors remained constant in subsequent passages. Responses of transplanted tumors growing in the flanks of syngeneic hosts to doses of radiation, methotrexate, or vinblastine were determined. Although the histologic appearances of the 5 squamous cell carcinomas were similar, tumor-doubling times and responses to irradiation and chemotherapeutic drugs were different. Small cell or large cell carcinomas were not observed.