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Production of Malignant Tumors in Rats with Radioactive Phosphorus^*

(From the Department of Pathology and Radiology, Western Reserve University School of Medicine, Clereland, Ohio)

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 LD₅₀ dose 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 40 per cent.

Atypical proliferation of bone was usually found in these rats, and the lesions may have served as a precursor to malignant change.

^* This work was performed under Contract No. W-31-109-eng-78 between the Atomic Energy Commission and Western Reserve University.

Received 10/17/49.