Carcinoma of the prostate in irradiated parabiotic rats.

Twelve hundred fifty-two pairs of male NEDH rats were parabiosed, one partner received a single dose of 1000 R X-radiation, and the other rat was shielded with lead. Eleven hundred twenty pairs survived over 200 days and constitute the basis of this report. Twenty-five of the irradiated partners developed malignant tumors of the prostate, 19 of which were adenocarcinomas. One adenocarcinoma appeared in the shielded partners and one in a control group of 586 parabiosed and single rats. The long-term effect of a single dose of 1000 R whole-body X-radiation is weakly carcinogenic for the rat prostate.