The overall objective is to characterize several types of hyperplastic lesions induced by chemical carcinogen in vivo and in vitro or arising spontaneously in untreated mammary glands of old female rats. Tumors will be characterized according to the mammary tissue of origin. Attempts will be made to enhance or inhibit tumor transformation in primary and transplantable mammary hyperplasias. The methodology will include mammary fat pad transplantation, organ culture, hormonal manipulation, and morphology.