Occurrence of Tumors, Particularly Mammary Tumors, in Agent-Free Strain C3HeB Mice

Abstract

The development of tumors has been studied in mice of substrain C3HeB which was produced by transfer of fertilized ova from strain C3H to strain C57BL. Mammary tumors occurred in 4 percent of virgin females of substrain C3HeB at an average age of 20.7 months, in 54.8 percent of breeding females at an average age of 19.2 months, and in 74.4 percent of force-bred females at an average age of 1 7.9 months. Mammary tumors occurred in 22.4 percent of C3HeB males, treated with diethyl-stilbestrol, at an average age of 15.0 months. Hepatomas occurred more frequently in animals of substrain C3HeB than have been observed previously in any other inbred strain. They were found in 58.6 percent of virgin females at an average age of 24.1 months, in 30.3 percent of breeding females at an average age of 21.0 months, in 37.8 percent of force-bred females at an average age of 20.5 months, in 55.1 percent of males, treated with diethylstilbestrol, at an average age of 23.3 months, and in 90.5 percent of breeding males at an average age of 21.4 months. Ovarian tumors occurred frequently in the females of substrain C3HeB: in 47.5 percent of virgin females at an average age of 24.3 months, in 37.4 percent of breeding females at an average age of 21.5 months, and in 29.3 percent of force-bred females at an average age of 21.6 months.