Furthermore, the relation of MMP-9 rs3918242 (allelic model, I2 = 26.8%, p = 0.255) in all populations with oral cancer risk was found; there was large heterogeneity regarding the associations of MMP-2 rs243865 (allelic model, I2 = 72.1%, p = 0.006; dominant model, I2 = 73.8%, p = 0.004) in all populations with LC risk and in Asians (dominant model, I2 = 63%, p = 0.067) with NPC risk, MMP-7 rs11568818 (dominant model, I2 = 52.8%, p = 0.12; recessive model, I2 = 52.7%, p = 0.121) in Asians with CC risk, and MMP-9 rs3918242 (allelic model, I2 = 63.3%, p = 0.028) in all populations with LC risk. The gene discussed is MMP9; the disease is nasopharyngeal carcinoma.