ALK and lung cancer: In some tumors, fusion genes have become recognized as a key factor in tumorigenesis, for example, BCR–ABL1 in chronic myelogenous leukemia, EWSR–FLI-1 in Ewing sarcoma, SYT–SSX in synovial sarcoma, NPM–ALK in lymphoma, ETV6–NTRK3 in breast cancer, TMPRSS2–ETS in prostate cancer, and EML4–ALK in lung cancer [6–11].