Among the 41 cases with negative p40 and TTF-1 and no obvious keratinization or glands, CK7 was positive (≥50% of the cells in all cases with any positivity) in 10 of the 12 AC, 7 of the 10 SqCC, 5 of the 8 LCC, 2 of the 8 neuroendocrine tumors and 2 of the 3 sarcomatoid carcinomas. The gene discussed is TTF1; the disease is sarcomatoid carcinoma.