In conclusion, this is the first study that has demonstrated the STAT3 gene promoter methylation and mRNA expression in 102 PA samples and analyzed the relationships between STAT3 gene epigenetic changes and patient clinical characteristics: age at the time of operation, gender, diagnoses of prolactinoma, acromegaly or Cushing syndrome, PA activity, recurrence and invasiveness. This evidence concerns the gene STAT3 and Cushing syndrome.