TTF1 and lung cancer: Immunohistochemical staining of the resected specimen showed a cytokeratin (CK) profile of CK7(+) and CK20(-), characteristic of pulmonary adenocarcinoma, while the tumor tissue was also positive for thyroid transcription factor (TTF)-1, a lung cancer marker, and negative for gross cystic disease fluid protein (GCDFP)-15, a breast cancer marker.