TTF1 and Merkel cell skin cancer: Further diagnosis is based on immunohistochemical staining, which differentiates MCC cells (CK20+, CD56+, CKAE1/AE3+, NSE+, PAX5+, NSP+, TdT+, SATB2+, TTF-1−, LCA−, S100−, p40−, chromogranin+/−, and synaptophysin+/−) from other cancer cells such as basal cell carcinoma, metastatic neuroendocrine carcinoma, lymphoma, or Ewing sarcoma.