The Effect of Neonatal Thymectomy on Lung Cancers Induced in Rats by Plutonium Dioxide

Neonatally thymectomized and intact outbred Wistar rats were exposed to plutonium dioxide aerosols, resulting in lung burdens that gave α-radiation doses to the lungs ranging from 100 to 1500 rad. While significant numbers of primary lung tumors were induced by the PuO2, no difference in lung tumor frequencies was observed in thymectomized compared to intact animals. However, thymectomized animals not receiving PuO2had an obviously increased frequency of extrapulmonary neoplasms. Since thymectomy did not result in any significant effect on lung tumor incidence, T-cell immunodepression probably should not be considered as a factor of risk for all individuals. Yet in animals with lung tumors, staging of cancers delineated an important effect of thymectomy, which was manifested as increased tumor sizes, enhanced tumor invasion, and a greater frequency of regional metastases.