The incidence of mammary gland carcinoma and cancer age in mice injected with estrogen and in noninjected mice of different strains.

Abstract

There exists in general a parallelism between the cancer incidence of the mammary gland in breeding control mice of various strains and the readiness with which the cancer rate can be increased in these strains in nonbreeding female mice or the occurrence of mammary gland carcinoma can be induced in male mice by injections of estrogen. This parallelism is due to the fact that in all of these cases we have to deal with the same mechanism; i.e. the production of carcinoma through the action of endogenous or exogenous ovarian hormones acting on a substratum with a definite inherited degree of growth tendency in the mammary gland. The proportion between cancer incidence in breeding and nonbreeding control mice varies greatly in different strains and these differences must be considered as due to an inherited strain characteristic a conclusion which confirms earlier observations made with different strains of mice. In breeding control mice belonging to strains with the highest incidence of mammary gland carcinoma the cancer rate was approximately as high in the 1st as in the later age classes. In strains with a weaker inherited tendency to the development of mammary gland carcinoma and in nonbreeding mice even of high tumor rate strains the cancer incidence increases in the direction from the 1st-3rd age class. This indicates that the earlier in life cancer in general appears the greater the intensity with which the causative factor acts. A similar relationship is observed in mice treated with exogenous estrogens--the stronger the dose injected and the greater the inherited tendency to cancer the earlier the mammary gland carcinoma appeared in the various strains. No significant difference in the incidence of this carcinoma was observed in male and nonbreeding female mice injected with large amounts of estrogen and belonging to strains with a strong hereditary tendency to the development of this type of cancer. (authors)