For IHC analysis, we used pancytokeratin (pan-CK), the most sensible and specific marker of generic epithelial lineage; TTF-1, typically positive in lung adenocarcinoma (but not in squamous cell carcinoma); and p40, which stains both squamous cell carcinoma (but not adenocarcinoma) samples and healthy bronchial cells (see Supplementary Figure S1A for staining controls). The gene discussed is TTF1; the disease is squamous cell carcinoma.