ABSTRACT
One hundred and ninety-six whole human breasts were examined by a subgross sampling technique with histologic confirmation. The method permitted the enumeration and identification of essentially all the focal dysplastic, metaplastic, hyperplastic, anaplastic, and neoplastic lesions. Completely suitable for analysis were 67 breasts obtained by autopsy, 29 cancerous breasts obtained by mastectomy, and 23 contralateral to those with cancer. All lesions, photographed subgrossly, were subsequently confirmed and correlated histologically. Morphologic evidence supported the hypothesis that lesions traditionally grouped as mammary dysplasia or fibrocystic disease arose in terminal ductal-lobular units (TDLU) with the probable exception of papillomas of ducts larger than terminal ones. Of the contralateral breasts, 60% with clinical cancer contained such lesions. An atypical lobule (AL) of type A (ALA) had the following characteristics: (a) it was more common in cancerous breasts or in those contralateral to cancer than in breasts not so identified; (b) it was a terminal structure on the mammary tree; (c) it tended to persist after the menopause, whereas normal lobules usually atrophied; and (d) as ALA progressed to DCIS, the unfolded lobule resembled a duct which gave the false impression that DCIS was a ductal lesion. The morphologic evidence supported the hypothesis that the lesions herein called AL were derived from TDLU and were precancerous.
