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Tumor Induction with Astatine-211 in Rats: Characterization of Pituitary Tumors^*

( Department of Pathology, Francis Delafield Hospital, Columbia University, New York, New York, and Laurence Radiation Laboratory, University of California, Berkeley, Calif.)

Inbred rats (W/Fu) of both sexes were given thyroid-destructive doses of astatine-211 (At²¹¹). A high incidence of pituitary tumors in both males and females so treated—64.7 and 55 per cent, respectively—was observed at 26 months of age.

Morphologic observations on the tumor hosts suggested that most, and perhaps all, pituitary tumors in this series were mammo-somatotropic. Transplantation of seven of the pituitary tumors was attempted, five with success. Four were mammo-somatotropic; the fifth is still under study.

Although the pathogenesis of induction of pituitary tumors and mammary tumors by At²¹¹ has not been clearly established, the present and earlier experiments indicate that direct irradiation played a major role in their induction. Thyroid destruction was compete in all rats but, unlike the results in radiothyroidectomized mice (in which pituitary tumors are invariably thyrotropic), all four pituitary tumors analyzed in transplantation studies were mammo-somatotropic.

The mammary tumor incidence was 65 per cent in the females and 5.9 per cent in the males at 26 months of age. Mammary tumors were diagnosed somewhat earlier than pituitary tumors. Nevertheless, stimulation by mammotropes probably played a significant role in mammary tumor induction.

^* This investigation was supported by C-6215 of the National Cancer Institute.

Received 11/15/63.