MUC5AC and ductal breast carcinoma in situ: Mucocele-like lesions (MLL) of the breast were originally described as benign lesions composed of multiple cysts lined by uniform flat to cuboidal epithelium with extravasated mucin, but subsequent reports described the coexistence of columnar cell lesions (CCL), atypical ductal hyperplasia (ADH) and ductal carcinoma in situ (DCIS).