When stratified by ethnicity, the pre-menopausal BC cases indicated significantly higher serum leptin levels than the controls in Asian population (SMD = 0.68, 95% CI = 0.47–0.89, P <.0001) or Caucasian population (SMD = 0.12, 95% CI = 0.09–0.44, P = .014). The gene discussed is LEP; the disease is breast cancer.