Novel and evolving therapies in the treatment of malignant phaeochromocytoma: Experience with the mTOR inhibitor everolimus (RAD001)

Phaeochromocytoma and paraganglioma are rare neuroendocrine tumours (NETS). They may be benign or malignant but the pathological distinction is mainly made when metastases are present. Available treatments in the form of surgery, chemotherapy, and radionuclide therapy may improve symptoms and biochemical markers, but the results for the control of tumour bulk are less favourable. Furthermore, responses to treatment are frequently short-lived. This short review outlines the main molecular and histological features of malignant phaeochromocytoma and the difficulties in differentiating between benign and malignant disease. We list current therapies used for malignant pheochromocytoma; however, these generally achieve relatively low success rates. Hence, there is a need for new and more effective therapies. In vitro studies have implicated the PI3/Akt/mTOR pathway in the pathogenesis of malignant NETS, including phaeochromocytoma. Everolimus (RAD001, Novartis UK) is a compound that inhibits mTOR (mammalian Target Of Rapamycin) signalling. We have used RAD001 in four patients with progressive malignant paraganglioma/phaeochromocytoma in addition to other therapies (with institutional approval for compassionate use), and evaluated the effects of this treatment. We outline these four cases and review the theoretical background for this therapy, although the outcomes were relatively disappointing.