Production of Malignant Tumors in Rats with Radioactive Phosphorus

One of the late effects observed in rats injected with large doses of radioactive phosphorus was the development of malignant neoplasms. Of thirteen tumors, ten were osteogenic sarcomas, situated most frequently in the jaw and also occurring in the spine, tibia, femur, or ilium. Four of the neoplasms metastasized to the lungs. There were three squamous-cell carcinomas involving the face and associated with exophthalmos. The neoplasms occurred in animals which received (a) a single LD₅₀dose of P³² (average latent period of 290 days) and (b) repeated doses of 1.5 μc. per gram of P³² (average latent period of 165 days). The incidence of tumor development was about 4C per cent. Atypical proliferation of bone was usually found in these rats, and the lesions may have served as a precursor to malignant change.