Figure 2. Hematoxylin-eosin staining of a transbronchial lung biopsy specimen from the left upper lobe mass revealing clusters of large atypical cells and areas of stratified growth, indicating a squamous cell carcinoma. Immunostaining was positive for p40 and cytokeratin 5/6 and negative for thyroid transcription factor-1 and napsin A. The final histological type could not be determined, and the pathological diagnosis was non-small cell carcinoma (×300).