We further analyzed the results by the lung cancer types, and the results showed that the serum leptin levels were not statistically different between the NSCLC group and the SCLC group (NSCLC: SMD=-0.53, 95%CI=-1.92–0.86, P=0.454; SCLC: SMD=-0.23, 95%CI=-0.64–0.18, P=0.270). The gene discussed is LEP; the disease is lung cancer.