Pulmonary neoplasms in rats that inhaled cerium-144 dioxide

The lung neoplasms induced in rats by inhaled, internally deposited 144CeO2 were described and classified using histologic criteria. F344 rats were exposed once or repeatedly by inhalation to 144CeO2 and observed for their life span. There was significant life shortening only in those rats with the highest radiation doses. In these rats, there was a high percentage of squamous cell carcinomas of the lung, as well as much lower percentages of adenocarcinomas of the lung, hemangiosarcomas of the lung, and pleural mesotheliomas. At lower doses, adenocarcinomas were the most predominant tumor. These adenocarcinomas were subdivided based on their histologic pattern: alveolar, papillary, tubular, or undifferentiated. Neither the mode of exposure (single or repeated) nor the sex of the rat influenced the lung tumor incidence or tumor type. The lung neoplasms induced by this beta-emitting radionuclide are similar in nature to those induced by alpha-emitting radionuclides deposited in the lung in rats. However, the radiation-induced squamous cell carcinomas of the lung differ from those induced by heavy particle loads of nonradioactive compounds. The radiation-induced squamous cell carcinomas occur in higher incidence and have a more malignant behavior than those induced by heavy particle loads.