The Incidence of Spontaneous Tumors in Female Mice (Breeders) of the CBA Strain

Abstract

The incidence of spontaneous tumors in female mice (breeders) of the CBA strain has been indicated in three recent papers (1–3). The purpose of dividing the observations into a series of individual experiments has been to eliminate any possible genetic variability as a source of varying tumor incidence. So far, two series (1, 2) of mice have been used for a moderate degree of breeding and then placed in reserve on a “mixed oatmeal diet”; a third series (3) of 63 females was similarly treated but continued throughout life on a commercially prepared diet.

The incidence of spontaneous tumors in the two series of mice kept on the oatmeal diet was similar (5.6 per cent and 3.7 per cent; average 4.8 per cent). The third series, kept on the commercial diet, showed a somewhat higher incidence, 12.7 per cent. In order to substantiate this possible difference in cancer incidence on different diets, a fourth series of 81 CBA females was placed in reserve between Dec. 13, 1934, and May 17, 1935, and continued on the commercial diet.

Experimental Observations

The ages of the 81 mice when the first litters were born are given in Chart 1. The average was 104.6 days. The ages at which the mice were separated from males and placed in reserve are given in Chart 2 (solid line).

Of the 81 female mice of the present series, 30 developed spontaneous tumors (Table I). Eighteen developed carcinoma of the mammary gland at an average age of 655.6 days; 6 developed hepatoma (4) at an average age of 695.0 days; 4 carcinoma of the ovary at an average age of 765.0 days; 2 primary carcinomas of the lungs at an average of 822.5 days; 1 an osteoid giant-cell sarcoma in the region of the ribs, at 925 days of life. Mouse S110171 was the only one in the series with more than one type of primary tumor. She developed a carcinoma of the mammary gland at 557 days of life. Autopsy at 590 days disclosed a hepatoma also. The incidence of spontaneous tumors in this series is, therefore, 37.0 per cent.