The effect of androgens and estrogens on spontaneous benign mammary tumors in the rat.

This article studies spontaneous benign mammary tumors in 97 female and male rats. All animals were observed until death and in every instance the tumors were examined and measured. In the 1st series of experiments autotransplants and homotransplants were done on 38 female rats by removing the original tumor and inserting fragments in the axillae and groins of the same animal; such serial autotransplantations were repeated from 2 to 5 times until the animal died. With minor variations such autotransplant tumors retained the structural identity of the original tumor. The 2nd series of experiments comprised 18 female rats injected with estrogen; large, spontaneous tumors showed no changes in morphology, but autotransplants and homotransplants grew more rapidly, and the latent period was reduced. A 3rd series of experiments was carried out with 16 female rats treated with androgens, which appeared to inhibit the epithelial components of adenofibromata. In a last series of experiments on 12 rats treated with estrogens and androgens together or in sequence, estrogen seemed to overcome the inhibiting action of androgens and exerted a stimulating effect on growing specific epithelium. Connective-tissue elements of the tumors did not appear to be directly affected by estrogens and to be moderately inhibited by androgens.