TTF1 and lung adenocarcinoma: Recently, enigmatic roles of TTF-1 have been noted: it appears to act as a “lineage-survival” oncogene and a protector against tumor progression in lung adenocarcinomas.16,17 These facts raise questions about the roles of TTF-1 in SCLC: Specifically, is TTF-1 a useful marker for SCLC location, or is TTF-1 expression a prognostic factor for SCLC?