CEACAM5 and neoplasm: Immunohistochemical analysis showed that the tumor cells were positive for cytokeratin 5/6 (CK 5/6) and calretinin, and negative for carcinoembryonic antigen (CEA), thyroid transcription factor-1 (TTF-1), cluster of differentiation 34 (CD34), and signal transducer and activator of transcription 6 (STAT6) (Fig. 3c–h).