Strain DD, a New High Mammary Tumor Strain, and Comparison of DD With Strain C3H

Abstract

Strain DD is a new high mammary tumor strain unrelated to other high mammary tumor strains in origin. It has the mammary tumor virus. Comparison is made between DD and our strain C3H which has the highest susceptibility to mammary tumors of any strain we know. The incidence of mammary tumors in DD is high, although not quite so high as in C3H, but, like in C3H, the incidence is high in virgin females as well as in breeders. Data presented show that strain C3HfB (C3H without the mammary tumor virus) continues to have a median incidence of mammary tumors in breeding females of a relatively old age, which we believe to be the result of high genetic susceptibility and hormonal stimulation from breeding in the absence of the mammary tumor virus. Reciprocal foster-nursing between DD and C3H and the use of fostered virgin C3HfB females for assay demonstrated that the mammary tumor virus of DD was weaker either qualitatively or quantitatively than that of C3H. There was no consistent evidence that the strains differed in their genetic susceptibility to the virus. The most interesting characteristic of females of DD is the progression and regression of some of their mammary tumors involving early plaque formation in relation to pregnancy, as described by others for strain RIII and RIII hybrids.