Evidence of oncogenic cofactors in radiation-induced tumors in mice

Five groups of 587 inbred female mice (WHC) were studied to determine the incidence of tumors as affected by irradiation of different areas. A dose of 400 rad of 60Co was given to all the groups. One group of 166 mice was total body irradiated, another group of 90 mice was irradiated in the upper-third portion of the body, another group of 93 mice was irradiated in the lower two-thirds of the body, and another group of 90 mice was half body irradiated on the right side. As control, a group of 148 nonirradiated mice was followed. The results showed a different incidence of cancer in mice, depending not only on the irradiated areas but also on the shielded ones. This suggested that other factors besides irradiation affect carcinogenesis.