MUC1 and ductal breast carcinoma in situ: This includes the presence of structures that indicate epithelial origin including ductal carcinoma in situ (DCIS), invasive breast carcinoma (IBC), no special type (NST), special type, or malignant squamous components, and/or demonstration of epithelial marker expression, including cytokeratin (CK), E-cadherin, and MUC1, on immunohistochemistry (IHC) [9, 10].