Following full-text screening, 88 studies were excluded due to irrelevant comparators (e.g., studies focusing on histone modifications without DNA methylation, immunohistochemical staining for MGMT, or transcription analysis without methylation data); inappropriate study design (e.g., conference abstracts, studies on chemotherapeutic effects, or narrative reviews not identified in the abstract stage); or unsuitable study population (e.g., pediatric studies or studies on intracranial tumors other than pituitary adenomas). Here, MGMT is linked to pituitary gland adenoma.