Among them, fourteen included articles regarding the association between the serum leptin levels and lung cancer [13–17, 20, 24, 25, 28, 29, 31–33, 37], and seven included articles about the association between the leptin expression levels in tissue and lung cancer [18, 21, 23, 26, 30, 35, 36]. This evidence concerns the gene LEP and lung carcinoma.