∗ Incidence of Mammary Cancer and Nature of the Sexual Cycle in Various Strains of Mice. †

Abstract

Loeb and Genther 1 studied the characteristics of the sexual cycle in 2 different strains of mice, which were believed to differ in their incidence of mammary cancer. Subsequently it became doubtful to what degree the cancer incidence differed in these mice, and further-more a comparison of only 2 strains of mice did not seem sufficient. Soon after completion of this first series, we began therefore a new and more extensive series of experiments. In the meantime there appeared communications by Lacassagne 2 and by Harde, 3 which seemed to establish a connection between the differences in the intensity of follicular hormone action during the sexual cycle and the incidence of mammary cancer. Quite recently, however, Bonser 4 in comparing 2 strains of mice differing in the incidence of spontaneous tumors did not find any correspondence between these 2 conditions.

Our own investigations are based on the study of 10 strains of mice markedly differing in their tumor incidence. We considered the following characteristics in the sexual cycle: (1) The duration of the sexual cycles and the number of cycles in individual mice, and the averages in the various strains. (2) The average duration of the periods of keratinization and the relation between the periods of oestrus and dioestrus in the various strains and in the individual mice composing them. (3) The degree of regularity of the oestrous cycles. We may summarize our results by stating that there was no parallelism noticeable between any of these factors and the incidence of mammary cancer either in the individual mice or in the whole strains.

We studied the effect of 2 different diets on the characteristics of the sexual cycle. In a first period of 30 days, the mice were fed solely on a diet of Purina Chow; in a subsequent period of 28 days the diet consisted of a mixture of chow, cracked corn and oats.