Our knowledge of the etiology of cancer of the breast has been greatly helped by experimental investigations on animals, especially mice. At the present moment at least three factors must be admitted as contributory to the production of cancer of the breast in mice: (1) the hereditary factor, (2) the estrogenic or ovarian factor and (3) the nursing or milk factor.
The experimental results pertinent to items 1 and 2 and directly related to our subject have been summarized by Halberstaedter1 as follows:
In strains which now show a high percentage of spontaneous mammary carcinoma, early castration of female mice reduces the incidence of carcinoma (Lathrop and Loeb2 and Cori3).
In strains which are characterized by a low percentage of spontaneous tumor the administration of estrogen to female mice increases the incidence of spontaneous carcinoma (Lacassagne 4).
Administration of estrogen induces the production of mammary carcinoma
HALBERSTAEDTER L, HOCHMAN A. THE ARTIFICIAL MENOPAUSE AND CANCER OF THE BREAST. JAMA. 1946;131(10):810-816. doi:10.1001/jama.1946.02870270010005