The 41 cases (6% of 657) with negative p40 and TTF-1 and no obvious keratinization or glands consisted of 12 AC, 10 SqCC, 8 LCC, 8 neuroendocrine tumors and 3 sarcomatoid carcinomas. The gene discussed is TTF1; the disease is leukoencephalopathy with calcifications and cysts.