MMP-9 rs3918242 was definitely relevant to breast cancer (BC) incidence among the overall populations (allelic model, OR = 1.281, 95% CI = 1.134–1.447, p < 0.001; dominant model, OR = 1.236, 95% CI = 1.065–1.434, p = 0.005; recessive model, OR = 1.681, 95% CI = 1.279–2.209, p < 0.001) and in Asians (allelic model, OR = 1.501, 95% CI = 1.263–1.785, p < 0.001; dominant model, OR = 1.526, 95% CI = 1.207–1.930, p < 0.001; recessive model, OR = 1.710, 95% CI = 1.262–2.317, p = 0.001) under three models. This evidence concerns the gene MMP9 and breast cancer.