Incidences of types of cancer in irradiated parabiont rats

A total body dose of 1000 R X radiation to 1252 male and 1366 female NEDH rats protected by permanent parabiosis to an untreated partner yielded respective cancer incidences of 42.7 and 38.3% within mean life-spans slightly less than single controls. These incidences were significant at the 1% level of probability compared with lower rates in shielded partners as well as in over 600 control parabiont partners and 700 single controls in which both sexes were nearly equally represented. Significant cancer incidences were induced in skin and islet cells of males, soft supporting tissue, renal tubules, bone of males and females, and ovary. Parabiosis per se provided local conditions conducive to the development of sarcomas, possibly enhanced by radiation, in anastomosed tissue as well as systemic changes promoting the spontaneous development of lymphoma and leukemia in females and inhibiting that of mammary carcinoma in females and malignant pheochromocytoma in males. The effects in females were largely canceled by radiation. The function of dose and its modification by factors contingent to parabiosis are discussed in relation to reported data on rats of other strains exposed to sublethal or lethal total-body X-ray doses