Mammary tumors in agent-free mice.

Abstract

This paper discusses tumors occurring in breeding females of 4 substrains of strain C3H mice deprived of the mammary tumor agent by foster nursing and designated as substrains C3Hf C3Hff C3Hf/2 and C3Hf/An. 22% of the 911 C3Hf females developed mammary gland tumors at an average age of 20 months. The tumors also occurred in 29% of the 118 C3Hff females at an average age of 19 months in 51% of the 72 C3Hf/2 females at an average age of 20 months and in 27% of the 96 C3Hf/An females at an average age of 20 months. In comparison 97% of the C3H breeding females developed mammary tumors at an average age of 7.8 months. No evidence of segregation of high-tumor lines was observed in the females with tumors in the 4 agent-free substrains. The incidence of mammary tumors was as high as or higher in daughters of mothers that died without mammary tumors than in those with mothers that later developed mammary tumors. A positive correlation was noted between the number of litters the C3Hf females produced and the incidence of mammary tumors; the incidences ranged from 2% in virgin females to 44% in females that had 7 litters each. The development of mammary tumors in these substrains is attributed to high genetic susceptivility the hormonal stimulation from breeding and the females advanced ages. Of the 311 mammary tumors occurring in these agent-free females 251 were adenocarcinomas of either type A or type B 1 was adenocarcinoma type C 53 were adenoacanthomas and 6 were carcinosarcomas.