MUC1 and squamous cell carcinoma: However, postoperative histopathological analysis (Figure 1D) unexpectedly revealed well-differentiated squamous cell carcinoma with positive surgical margins (carcinoma present at resection margins), supported by characteristic immunohistochemical findings: strong diffuse positivity for pan-cytokeratin (CK, +++), CK5/6 (+++), p63 (+++), and p40 (++); strong membranous expression of epithelial membrane antigen (EMA, +++); focal CD15 reactivity (+); and a markedly elevated Ki-67 proliferative index of 60%.