The importance of MUC1 cellular localization in patients with breast carcinoma - An immunohistologic study of 71 patients and review of the literature

BACKGROUND. The MUC1 mucin is present on the apical surface of normal secre tory epithelia. In breast carcinoma, MUC1 expression is variable in amount and cellular localization, the significance of which is controversial. The authors undertook a detailed analysis of staining pattern combined with a c omprehensive literature review to better understand the role of MUC1 in bre ast carcinoma. METHODS. Seventy-one patients with breast carcinoma were examined for MUC1, beta -catenin, and E-cadherin staining patterns. These data were compared with data from 25 articles from the literature examining the expression of MUC1 in breast carcinoma. RESULTS, All invasive carcinomas showed some MUC1 staining. In invasive duc tal carcinomas, MUC1 was detected in the apical membrane (15%), cytoplasm ( 93%), or circumferential membrane (13%), with 81% of tumors showing a mixtu re of patterns. Tumors with low overall MUC1 expression (less than or equal to 50% positive tumor cells) had a higher nuclear grade than tumors with h igh overall MUC1 expression (> 50%; P = 0.01). Tumors with high and low cyt oplasmic expression had no difference in nuclear grade (P > 0.3). Circumfer ential membrane staining was correlated with positive lymph node status (P = 0.011). CONCLUSIONS. In the literature, similar findings prevailed in which overall MUC1 expression was increased in lower grade (10 of 14 studies), estrogen receptor positive (8 of 13 studies) tumors and was associated with a better prognosis (8 of 13 studies). High cytoplasmic staining was associated with a worse prognosis, an association that was not explained by differences in histologic grade. Thus, the presence of MUC1 in the majority of tumor cell s is associated with better differentiated tumors and with an improved prog nosis. However, aberrantly localized MUC1 in the tumor cell cytoplasm or no napical membrane is associated with a worse prognosis. Cancer 2001;91:1973- 82, (C) 2001 American Cancer Society.