BDNF and lung cancer: Previous studies have reported that 9 out of the 15 immune genes associated with prognosis (S100A16, CRABP1, RBP2, FGF2, FPR2, BDNF, ANGPTL4, SEMA4B and VIPR1 [33, 34, 35, 36, 37, 38, 39, 40, 41]) are involved in the pathogenesis of lung cancer.