Mucocele-like tumor (MLT) of the breast is a mucinous disorder that is generally difficult to distinguish from mucinous carcinoma. Moreover, MLT is often accompanied by atypical ductal hyperplasia (ADH) or ductal carcinoma in situ (DCIS), and preoperative diagnosis is very confusing. In this paper, we summarize the clinicopathological characteristics of six cases of MLTs, comparing them with mucinous carcinoma. MLTs were characterized by clustered, coarse calcification on mammography and clustered, hypoechoic lesions with or without echogenic spots on ultrasonography. On fine-needle aspiration cytology (FNAC), three cases were correctly diagnosed and three cases were judged to be indeterminate, or insufficient material was present. Ultimately, excisional biopsies were performed to obtain a correct diagnosis in all cases. Immunohistochemical staining of MLTs accompanied by ADH or DCIS (malignant MLTs) revealed the presence of MUC6, while MLTs without ADH or DCIS (benign MLTs) were MUC6-negative. At present, as it is difficult to detect small areas of DCIS adjacent to the MLT by FNAC, excisional biopsy is essential. Immunohistochemical staining for MUC6 may be useful in differentiating between benign MLTs and malignant MLTs, although further investigation is needed.
Mucocele-like tumor Mucinous carcinoma Breast cancer Immunohistochemical staining