OBJECTIVETo study the clinicopathologic features, immunophenotype and differential diagnosis of cystic hypersecretory lesion (CHL) of the breast.

METHODSClinicopathologic and follow-up data of six cases of breast CHL in 2010-2013 were collected and reviewed.Immunohistochemical and mucinous staining was performed.

RESULTSAll six patients were female, age ranged from 37 to 71 years (average 49.3 years). Three cases were cystic hypersecretory hyperplasia (CHH), the other three cases were cystic hypersecretory carcinoma (CHC). Clinically the lesions presented as either breast mass or mammographic calcification.Grossly, the cystic hypersecretory lesions were poorly circumscribed, with multiple colloid containing cysts on the cut surface. Microscopically, the remarkable feature was numerous enlarged cysts which contained densely eosinophilic homogeneous secretion similar to the colloid seen in thyroid follicles, and calcification was seen in the cyst in one case. The secretion was D-PAS and mucicarmine positive. The lining epithelium of the cysts was uniformly flat, cuboid or columnar, and arranged in a monolayer. The cells may be arranged in turfs, solid or micropapillary patterns in CHH.In cases with dysplasia, the epithelium showed cytological and structural atypia, but the usual morphology of atypical dutal hyperplasia such as arcades, rigid bridges or cribriform pattern was less common. The three CHC included two invasive ductal carcinomas (IDC) and one ductal carcinoma in situ (DCIS).In CHL, there was immunoreactivity to S-100 protein, CK5/6 and CK14.Of the three CHCs, ER and PR were expressed in only one IDC.No HER2 expression was identified in the two invasive CHCs.One patient was lost to follow-up, and the rest were uneventful at 18 months.

CONCLUSIONSCHL of the breast is a rare pathological entity. Multiple colloid-filled cysts is a unique histological feature. The epithelium of CHL may show usual hyperplasia, dysplasia or carcinoma.