We did not observe co-expression of TTF-1 and Napsin A in our series of colorectal carcinomas, and only in 2 out of 419 gastric (0.5%) and 3 out of 125 esophageal cancer cases (2.4%), thereby potentially decreasing the rate of tumor misinterpretation when using both antibodies to distinguish them from lung adenocarcinomas. The gene discussed is TTF1; the disease is neoplasm.