Non-functioning pituitary adenomas account for approximately 30% of all pituitary adenomas and are the most common type of benign pituitary tumor. Many incidental findings of non-functioning adenomas cause no clinical symptoms at all and may not require treatment, but require close observation and follow-up. Nonfunctional adenomas are usually large and may cause compression of the optic nerve and abnormal endocrine function of the pituitary gland. Some non-functioning adenomas are aggressive and can destroy their surrounding structures, causing more damage.
Temozolomide (TMZ) is a cytotoxic alkylating agent that methylates the O-6 site of DNA guanine and also inhibits angiogenesis in tumor tissues. Hagen et al. used TMZ treatment (150-250 mg/M2 body surface area for 5 consecutive days each, 23 days apart) in one pituitary cancer and two invasive pituitary adenomas (PRL and non-functional adenoma, respectively). The results showed that all three patients had significant tumor shrinkage and normalization of hormone levels. Moreover, all three patients had MGMT that was not expressed or was lowly expressed. Widhalm et al. analyzed 24 cases of aggressive, recurrent non-functional adenomas and found that the percentage of MGMT(-) was 50%, which was higher than that of the general population (24%). This study suggests that aggressive, recurrent non-functional adenomas may be suitable for treatment with TMZ. In addition, there are many case reports of treatment of aggressive pituitary adenomas of various pathological types with TMZ, all showing that TMZ significantly controls tumor growth and stabilizes hormone levels, and that this effect is dependent on the absence or low expression of MGMT.