Heredity and Internal Secretion on Origin of Mammary Cancer in Mice.

More than 20 years ago Loeb in preliminary investigations on the heredity of cancer in mice first applied to the analysis of this problem a method which allowed the establishment of the significance of heredity in mice on a much more secure basis than was possible by the use of the statistical methods similar to those employed in the study of the influence of heredity in human cancer. This method consisted in the breeding of separate families and strains of mice in the same breeding establishment and in the study of the cancer rate in successive generations of strains which had thus been kept under similar conditions as far as the outer environment was concerned. By this method he found in cooperation with Miss Lathrop that heredity was a factor of very great significance in the origin of cancer of mice. 1 While certain strains had a cancer rate approaching zero, other families had a rate approaching 80% or more. In successive generations these differences between different strains remained approximately constant.

However, in the further analysis of the causes of mammary cancer in mice we found that in addition to heredity, the functional activity of the sex organs played a significant part in the origin of cancer of mice. We found that the prevention of mice from breeding lowered the cancer rate definitely and that in different strains the effect of the prevention of breeding differed in intensity. However, we found castration of the mice to be of even greater significance and moreover the effect of castration was the greater, the earlier the ovaries were removed. A quantitative relation was thus established between the internal secretion of the ovary and the frequency with which cancer appeared in the breast of mice. The growth stimuli emanating from the ovary and affecting rhythmically the mammary gland acted thus in a similar quantitative manner to tar, which when applied experimentally to the skin also produced cancer the more frequently and the earlier, the earlier and oftener the tar had been used. In both cases, cancer would develop a long time after these 2 types of stimuli had ceased to act. Stimuli developing in the outer and inner environment acted therefore in a similar manner in the causation of cancer. These latter investigations were subsequently confirmed and extended by Cori. 2