Mucin expression in mucinous carcinoma and other invasive carcinomas of the breast.

To investigate mucin expression in breast cancer, immunohistochemical staining was performed on 30 mucinous carcinomas and 95 non-mucinous invasive carcinomas. MUC2 expression was detected in all mucinous carcinomas, but only in 11.1% of invasive ductal carcinomas, and in none of the invasive lobular carcinomas and medullary carcinomas. MUC1 is often expressed in invasive breast carcinoma, but not in medullary carcinoma. Strong cytoplasmic staining was seen in invasive ductal carcinoma, in contrast to surface membrane staining in mucinous carcinoma and intracytoplasmic vacuole staining in invasive lobular carcinoma. CA19-9 and CA50 expression in more than 25% of tumor cells was seen in 17.2 and 16.0% of invasive ductal carcinomas, respectively, but not in mucinous carcinomas. CA125 and human gastric mucin were rarely expressed in breast cancer, irrespective of histologic type.