To date, ~30 cases of pituitary adenoma have been treated with temozolomide (including ten ACTH-secreting adenomas). Overall reported response rate is approximately 60 % [62, 63]; however, information on temozolomide treatment of pituitary adenomas is currently confined to individual case reports and three case series [65–67]. An inverse relationship between tumoral O6-methylguanine-DNA methyltransferase (MGMT) immunoexpression and response to temozolomide therapy has been suggested, but not confirmed in all studies [62, 65, 67, 68].