Strain-limited Development of Tumors of the Pituitary Gland in Mice Receiving Estrogens *

Hypophyseal tumors occur rarely in mice. Only one mouse among 11,000 autopsied in Dr. Slye's laboratory showed a hypophyseal tumor.11 A chromophobe-cell adenoma of the pituitary gland was reported in a mouse which had bilateral granulosa-cell tumors of the ovaries.6 This animal also showed evidence of hyperestrogenic stimulation, as indicated by multiple mammary tumors and uterine glandular cystic hyperplasia. Generalized hypertrophy of the pituitary gland occurs frequently in rats and mice receiving estrogens.9 Almost simultaneously three groups of investigators reported hypophyseal adenomatous hypertrophy or adenomas in rats or mice receiving estrogens in large amounts over long periods.'2 On the other hand, such tumors were not observed among 11 1 mice of 3 different strains (A, CBA, and C3H) given estrogens,4 while, in another laboratory,l one tumor was found among 679 mice. Lacassagne'0 ascribed an initial failure to observe hypophyseal lesions to a contamination of the "folliculin" benzoate he used with equilin or equilenin. Recently, Zondek'4 described large tumors of the pituitary gland in rats given large amounts of estrogens over a period of from 7 to 9 months. Some of these tumors weighed more than 300 mg.