Immunohistologically, the tumor cells were stained positive for cytokeratin 7 (CK7) in the cytoplasm and for thyroid transcription factor 1 (TTF-1) in the nucleus, but negative for cytokeratin 20 (CK20), suggesting that the tumor cells originated from either thyroid cancer or lung adenocarcinoma. This evidence concerns the gene KRT7 and thyroid gland carcinoma.