Pathological evaluation of the excised tissues revealed metastatic, poorly differentiated sarcomatoid carcinoma with immunohistochemical staining positive for pan-cytokeratin, vimentin, carbonic anhydrase IX (CA-IX), cytokeratin 7 (CK7), and thyroid transcription factor 1 (TTF-1), highly consistent with a pulmonary primary (Figure 3, panels A-D). The gene discussed is CA9; the disease is sarcomatoid carcinoma.