The tumor cells exhibited positivity for cytokeratin 7 (CK7) and caudal type homeobox 2 (CDX-2) but negativity for cytokeratin 20 (CK20), paired box 8 (PAX8), NK3 homeobox 1 (NKX3.1), and thyroid transcription factor 1 (TTF-1) (Figure 4B). This evidence concerns the gene PAX8 and neoplasm.