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Effect of Chronic Exposure to Fast Neutrons on the Development of Mammary Tumors in the Rat^*

Quentin L. Hartwig, Sidney P. Kent and James A. Sproul, Jr.

( Department of Radiobiology, School of Aviation Medicine, USAF, Randolph Air Force Base, Texas)

Fifty Sprague-Dawley rats were chronically exposed for 6 months to 154 rep of fast neutrons delivered at a dose rate of 87.2 mrep/hour, and 50 served as controls.

Sixty-eight per cent of the irradiated rats developed one or more tumors, as compared with 14 per cent in the controls. Malignant tumors were found in 32 per cent (11/34) of the irradiated rats with tumors, 36 per cent (4/11) of which had metastasized. No metastasis occurred in the controls. Most of the tumors in the irradiated and control animals developed in the mammary glands.

The results suggest that, after exposure to chronic neutron radiation, benign tumors develop randomly throughout the life span of the animals, whereas malignant tumors are more apt to appear soon after the exposure period.

This experiment suggests that a 6-month chronic exposure to 154 rep of fast neutrons can accelerate the onset of mammary gland tumors in the Sprague-Dawley rat and increase their frequency.

^* This work was conducted at the Radiobiological Laboratory of the University of Texas and the United States Air Force, Austin, Texas, and was supported (in part) with funds provided under Contract AF41(657)-149 and the School of Aviation Medicine, USAF.

Present address: Department of Surgery, Louisiana School of Medicine, New Orleans, Louisiana.

Present address: Department of Pathology, University of Alabama, Medical Center, Birmingham, Alabama.

Present address: Oak Ridge National Laboratory, Biology Division, P. O. Box P, Oak Ridge, Tennessee.

Received 5/ 6/57.