Mammary tumorigenesis in chemical carcinogentreated mice. II. Dependence on hormone stimulation for tumorigenesis

mice were treated with 7,12-dimethylbenz[a]anthracene (DMBA) or urethan to determine conditions that would Induce a high frequency of ductal hyperplaslas in the mammary gland. Among virgin BALB/c mice treated with either 3.0 or 4.0 mg DMBA, ductal hyperplasias and mammary tumors were present in 50"10 and 31"10 of the mice, respectively. These ductal hyperplasias were char-acterized by intraluminal epithelial hyperplasia and capped by endbud·llke structures that appeared abnormal. Hyperplastic al-veolar nodules were not seen. Most mammary tumors were ade-nocarcinomas rather than the adenoacanthomas observed in DMBA-treated, pituitary isograft-bearing BALB/c mice. The pre-dominant mammary lesions in urethan-treated, pituitary isograft-bearing C57BL and (C57BL x DBAf)F, mice were terminal duct (lobular) hyperplaslas characterized by Intraluminal epithelial hy-perplasia; the urethan-induced mammary tumors were a mixtur