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Further Studies on the Incidence of Lymphomas in Mice Exposed to X-Rays and Given Sex Hormones^*

( Department of Anatomy, Yale University School of Medicine, New Haven, Conn.)

1. Whole-body roentgen irradiation (285–380 r at one exposure) is lymphomogenic in mice of the "BC" strain. The incidence of lymphomas was approximately 3 times greater in females than in males.

2. Testosterone propionate, when given subsequent to roentgen irradiation, inhibited the lymphomogenic action of x-rays. Estradiol benzoate augmented the incidence, especially in males.

3. Untreated control mice of the same strain showed an incidence of mediastinal lymphomas of 1.4 per cent. Reticulosarcomas occurred more frequently (6.5 per cent) in the controls than in the irradiated mice (3 per cent). In both groups these tumors occurred in the older animals.

4. A unique organization of the reticulum of the mediastinal lymphomas was described.

5. Sarcomas of the spindle-cell or fibrous type appeared in 20–30 per cent of the irradiated male mice given weekly subcutaneous injections of sesame oil or testosterone propionate dissolved in sesame oil. These tumors usually appeared in mice over 500 days old.

6. Three mice over 500 days old had adrenal medullary tumors.

^* These investigations were supported in part by the Jane Coffin Childs Memorial Fund and the National Cancer Institute of the United States Public Health Service, Grant C-343-C6.

Received 10/17/53.