MUC1 and neoplasm: On immunohistochemical staining, the tumor cells were positive for gross cystic disease fluid protein (GCDFP)-15 (Figure 3A), cytokeratin (CK) 7, and epithelial membrane antigen (EMA), and negative for CK20, S-100 protein, estrogen receptor (ER), and progesterone receptor (PR) (Table 1).