Aggressive and Metastatic Pituitary Neuroendocrine Tumors: Therapeutic Management and Off-Label Drug Use

Abstract

Pituitary neuroendocrine tumors (PitNETs) are the most common pituitary tumors and the second most common brain tumors. Although the vast majority (>90%) are benign, a small percentage (<2%) are aggressive. These aggressive PitNETs (AgPitNETs) are defined by the presence of radiological invasion, a high rate of cell proliferation, resistance to conventional treatments, and/or a high propensity for recurrence. Lastly, there are the rare pituitary carcinomas, also known as metastatic PitNETs (MetPitNETs), which account for only 0.2% of cases and are defined by the presence of craniospinal or distant metastases. At present, there are no definitive factors that allow us to predict with certainty the aggressive behavior of PitNETs, making the therapeutic management of AgPitNETs a real challenge. Surgery is considered the first-line treatment for AgPitNETs and MetPitNETs. Radiation therapy can be effective in controlling tumor growth and regulating hormone hypersecretion. Currently, there are no approved non-endocrine medical therapies for the management of AgPitNETs/MetPitNETs, mainly due to the lack of randomized controlled clinical trials. As a result, many of the medical therapies used are off-label drugs, and several are under investigation. Temozolomide (TMZ) is now recognized as the primary medical treatment following the failure of standard therapy (medical treatment, surgery, and radiotherapy) in AgPitNETs/MetPitNETs due to its ability to improve overall and progression-free survival rates in responding patients over 5 years. Other therapeutic options include pituitary-targeted therapies (dopamine agonists and somatostatin analogs), hormonal antisecretory drugs, non-hormonal targeted therapies, radionuclide treatments, and immunotherapy. However, the number of patients who have undergone these treatments is limited, and the results obtained to date have been inconsistent. As a result, it is imperative to expand the cohort of patients undergoing treatment to better determine the therapeutic efficacy and safety of these drugs for individuals with AgPitNETs/MetPitNETs.