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Figure 1: Immunohistochemistry stains in squamous cell carcinoma and adenocarcinoma of lung. H&E: hematoxylin and eosin; CK: cytokeratin; TTF-1: thyroid transcription factor 1. Squamous carcinomas are typically positive for CK5/6 and P63, and negative for CK7 and TTF-1, with the reverse profile for adenocarcinoma although this case of squamous cell carcinoma demonstrates focal weak staining for CK7.