On the Relation between the Incidence of Mammary Cancer and the Nature of the Sexual Cycle in Various Strains of Mice

Abstract

In a series of earlier investigations it has been shown that in different strains of mice kept under the same environmental conditions, the incidence of mammary cancer may vary from almost 100 per cent to zero. Each strain has its characteristic tumor incidence, which remains approximately constant in successive generations. Heredity is therefore an important factor in the origin of mammary cancer in mice (1). In addition to heredity, a second factor was found to be necessary for the development of mammary tumors, namely the action of ovarian hormones. The length of time during which the hormones (presumably follicular) were allowed to act on the mammary gland was shown to bear a quantitative relation to tumor incidence, as well as to the period of life at which cancer developed; the longer the hormones were allowed to act on the mammary gland, the greater was the number of mice in which cancer occurred and the earlier it appeared (2). A parallelism was therefore apparent between the influence of internal secretion on the origin of mammary cancers and the effect of various external stimulants of a chemical and physical nature. The relation between the internal secretion or external stimulation and hereditary factors in the development of cancer could be expressed by the equation: S + H or S × H = C, in which S signifies the external or internal stimulating endocrine factors; H signifies heredity, and C the intensity factor in the origin of cancer, including its frequency and time of appearance.