NKX2-1 and lung cancer: In addition to genes associated with smoking the AC1/AC2 classifier included several genes implicated in lung cancer tumorigenesis, such as KITID1MMP7MYCNXRN2, and CYP24A1, as well as type II pneumocyte marker genes such as NKX2-1 (TTF1/TITF1), LAMP3 (CD208), and surfactant proteins SFTPB and SFTPC (in Additional file 1: Table S1).