Stratification by sample size showed HCC group had significantly higher leptin levels than CFC group in both small (n < 100) sample numbers (SMD = 1.57, 95% CI (0.22, 2.91), P = 0.022) and large (n ≥ 100) sample numbers (SMD = 2.23, 95% CI (1.21, 3.26), P = 0.000). Here, LEP is linked to hepatocellular carcinoma.