Significance of MUC1 and β-Catenin Localization in Mucinous Carcinoma of the Breast

Background/aim: There are two main subtypes of mucinous carcinoma (MC) based on the quantification of the mucinous component: the pure variant (pMC) and the mixed variant (mMC). pMC has been subdivided into pure A with a hypocellular variant, and pure B with a hypercellular variant.

Patients and methods: We retrospectively analyzed the clinicopathological features of 99 patients with MC who were treated at our institution from January 2002 to December 2014. We evaluated the expression profiles of markers, including mucin (MUC) family members, in the patients groups representing different MC subtypes by performing immunohistochemistry to identify factors involved in the differentiation and progression of MCs.

Results: Among the 99 patients, 76 (76.8%) had pure mucinous carcinomas (pMC) and the other 23 (23.2%) had mixed mucinous carcinomas (mMC). Of the pMCs, 54 were pure A and 22 were pure B. The prognosis was worse for pure B than pure A and worse for mMC than pMC. Although there was no significant difference in clinicopathological factors between the pure A and pure B groups, immunohistochemical staining revealed differences in the localization of mucin MUC1 and β-catenin. A comparison of the pMC and mMC cases revealed more lymphovascular invasion in mMC and differences in the localization of β-catenin between the two groups.

Conclusion: The patients' prognoses were significantly poorer depending on the histologic subtype (in the order pure A, pure B, and mixed). MUC1 localization and β-catenin were revealed as independent predictors contributing to the poorer prognosis.