TTF1 staining is a critical single marker for adenocarcinoma in lung cancer, with Napsin A also showing some diagnostic utility as a secondary marker for adenocarcinoma in lung tumors (62); a combination of TTF1 and Napsin A may yield greater sensitivity for lung adenocarcinoma (63), and the absence of both TTF1 and Napsin A immunoreactivity played a pivotal role in solidifying the diagnosis for the cases. The gene discussed is TTF1; the disease is lung adenocarcinoma.