Mammary and other tumors as a response to radiation and multiple stresses.

Parabiosis of paired NEDH rats and subsequent irradiation of one produced multiple stresses, particularly altered hormonal milieu. Benign mammary tumors developed in 8.6% of the control pairs, 12.7% of the shielded partners, and 19.7% of the irradiated rats. Mammary cancers developed in 5% of control pairs, 14.2% of the shielded partners, and 11.9% of the irradiated rats. With increased amounts of prolactin, the rate was 50% in shielded partner, 10% in the irradiated rats. Mesenchymal sarcoma develop at the anastomosis in parabiont rats. Their incidence rate in single controls is 3.1%, in parabiont control pairs 12.5%, in pairs with one partner irradiated 16.6%, and with both irradiated 23.1%. The incidence rate in other parts was increased threefold over controls in the irradiated partners. Radiation appears to be the dominant factor in both mammary and anastomotic tumors.