Altered mucin expression is a field change that accompanies mucinous (colloid) breast carcinoma histogenesis

Mucinous carcinomas of the breast, so-called colloid carcinomas, exhibit be tter prognoses than their nonmucinous breast counterparts. This biological difference exhibited by mucinous breast carcinomas prompted us to examine t he relationship of mucin expression to colloid carcinoma histogenesis. We s tudied 50 colloid carcinomas, 50 noncolloid cancers, and 50 normal breasts by hematoxylin-eosin (H&E) and Alcian blue staining, mucin immunohistochemi stry, in situ hybridization with a battery of MUC riboprobes, and ancillary digital image analysis. We observed luminal mucin in normal ducts in 80% o f colloid carcinomas compared with 10% of noncolloid carcinomas and 6% of n ormal breasts (P < .01). In the cases of colloid carcinoma that showed muci n-filled ducts, luminal mucin was observed in 40% of the normal ducts and a cini, 40% to 75% of the ducts involved by hyperplasia, atypical ductal hype rplasia (ADH) and ductal carcinoma in situ (DCIS), respectively, and in 50% of the co-incidental areas of cysts (mucoceles), adenosis, fibroadenoma, a nd intraductal papilloma (P < .01). Immunohistochemistry showed that colloi d carcinomas showed strong MUC2 cytoplasmic immunoreactivity and decreased MUC1 immunoreactivity compared with noncolloid carcinomas. In situ hybridiz ation studies indicated fivefold increased MUC2 signals and twofold increas ed MUC5 signals within adjacent and remote normal epithelium in only the co lloid carcinoma cases (P < .01; P < .05). In these cases of colloid carcino ma, these increased MUC2 and MUC5 signals were also observed in areas of hy perplasia, ADH, DCIS, and invasive carcinoma. In contrast, the noncolloid c arcinomas showed fivefold increased MUC1 signals but no increases in MUGS o r MUC5. In mixed colloid/noncolloid carcinomas, the colloid areas had ident ical mucin expression patterns as the pure colloid carcinomas, but there wa s a loss of MUC2 and MUC5 expression and a gain of MUC1 expression in the n oncolloid areas that was therefore identical to the pattern observed in pur e noncolloid carcinoma. In this study, we conclude that the altered express ion of mucin so characteristic of colloid carcinoma is also a field change present in adjacent and remote normal breast epithelium. HUM PATHOL 29:1517 -1523. Copyright (C) 1998 by W.B. Saunders Company.