MGMT and head and neck squamous cell carcinoma: The overall OR was changed from 2.68 (95%CI, 2.13–3.38) to 3.27 (95%CI, 2.57–4.16) under the fixed effects model by omitting each single study, which demonstrates that the pooled OR between the MGMT promoter methylation and risk of HNSCC was reliable and stable (Fig 3).