Expression of mucins (MUC1, MUC2, MUC5AC and MUC6) in mucinous carcinoma of the breast: comparison with invasive ductal carcinoma.

AIMS: Mucinous carcinoma of the breast usually shows less frequent lymph node metastasis and more favourable outcome compared with invasive ductal carcinoma. The aim of this study is to compare the expression profiles of several mucins in mucinous carcinomas and invasive ductal carcinomas to gain insight into the relationship between the less aggressive biological nature of mucinous carcinoma and the role of mucins.

METHODS AND RESULTS: We examined the expression profiles of MUC1 (membrane-bound mucin) of different glycoforms (from non-glycosylated form to fully glycosylated form), MUC2 (intestinal type secretory mucin), MUC5AC (gastric surface type secretory mucin) and MUC6 (gastric pyloric gland type secretory mucin) in 17 mucinous carcinomas and 46 invasive ductal carcinomas using immunohistochemistry. Various glycoforms of MUC1 were expressed frequently in both mucinous carcinomas (65-100%) and invasive ductal carcinomas (92-100%), although non-glycosylated MUC1 (MUC1/CORE) and fully glycosylated MUC1 (MUC1/HMFG-1) showed significantly lower expression rates in mucinous carcinomas compared with those in invasive ductal carcinomas. The expression rates of MUC2 (94%) and MUC6 (71%) in mucinous carcinomas were significantly higher than those of MUC2 (15%) and MUC6 (15%) in invasive ductal carcinomas. There was no significant difference in the expression rate of MUC5AC in mucinous carcinomas (12%) and that in invasive ductal carcinomas (4%).

CONCLUSIONS: The expression rate of MUC1/CORE and MUC1/HMFG-1, which is related to poor prognosis in the gastric and colorectal cancers, is low in mucinous carcinomas. The high expression rate of gel-forming secretory mucins (MUC2 and MUC6) in mucinous carcinoma suggests that high production of these types of mucins may act as a barrier to cancerous extension resulting in their less aggressive biological behaviour.