Expression of MUC1, MUC2, MUC5AC and MUC5B in mucinous lesions of the breast.

OBJECTIVE The purpose of this study was to investigate the expression of MUC1, MUC2, MUC5AC and MUC5B in breast mucinous lesions. METHODS Immunohistochemical staining of MUC1, MUC2, MUC5AC, MUC5B and synaptophysin was performed in 78 cases of mucinous carcinoma (MC), 36 cases of mucocele-like lesions (MLL) and 13 cases of solid papillary carcinoma (SPC). MC was classified as type A or type B and MLL was classified as MLL, MLL with atypical ductal hyperplasia and MLL with ductal carcinoma in situ. RESULTS MUC1 was expressed in MC type A and MLL with luminal/apical pattern, while MC type B and SPC showed membrano-cytoplasmic expression of MUC1 (p < 0.001). A luminal/apical or luminal/apical + cytoplasmic pattern of MUC2 expression was observed in MC type A, while MC type B and SPC showed membrano-cytoplasmic MUC2 expression (p < 0.001). On MUC5B staining, MC type A and MLL were negative, while MC type B and SPC showed membrano-cytoplasmic expression (p = 0.011). The positive rate for synaptophysin was higher in MC type B and SPC than in MLL and MC type A (p = 0.001). CONCLUSIONS Similar MUC phenotypes were observed between MLL and MC type A and between MC type B and SPC.