Mucocele-like tumor of the breast caused by ductal carcinoma in situ: a case report.

A mucocele-like tumor (MLT) of the breast caused by clinging and micropapillary carcinoma in situ is reported. The tumor was a smooth-contoured mass located near the nipple in the lower inner quadrant of the left breast. Ultrasonography showed a cystic tumor and distended ducts. An aspiration specimen contained abundant mucinous material and a small amount of epithelial cell components, but was insufficient for cytological diagnosis. An excisional biopsy specimen disclosed multiple cysts containing mucin with extravasation into the stroma. Additional pathologic diagnosis using consecutive microscopic sections demonstrated ductal carcinoma in situ. Subcutaneous mastectomy was subsequently performed. Histopathologic findings in the resected and biopsy specimens indicated a diagnosis of MLT caused by widely spreading clinging and micropapillary ductal carcinoma in situ. The ductal epithelium of the MLT in an open biopsy specimen must be carefully examined using consecutive microscopic sections to detect occult DCIS.