Therapy of endocrine disease: the challenges in managing giant prolactinomas

Giant prolactinomas are rare tumours, representing only 2-3% of all prolactin (PRL)-secreting tumours and raising special diagnostic and therapeutic challenges. Based on several considerations developed in this review, their definition should be restricted to pituitary adenomas with a diameter of 40  mm or more, significant extrasellar extension, very high PRL concentrations (usually above 1000  μg/l) and no concomitant GH or ACTH secretion. Giant prolactinomas are much more frequent in young to middle-aged men than in women, with a male to female ratio of about 9:1. Endocrine symptoms are often present but overlooked for a long period of time, and diagnosis is eventually made when neurologic complications arise from massive extension into the surrounding structures, leading to cranial nerve palsies, hydrocephalus, temporal epilepsy or exophthalmos. PRL concentrations are usually in the range of 1000-100,000  μg/l, but may be underestimated by the so-called 'high-dose hook effect'. As in every prolactinoma, dopamine agonists are the first-line treatment allowing rapid alleviation of neurologic symptoms in the majority of the cases, a significant reduction in tumour size in three-fourths of the patients and PRL normalization in 60-70%. These extensive tumours are usually not completely resectable and neurosurgery has significant morbidity and mortality. It should therefore be restricted to acute complications such as apoplexy or leakage of cerebrospinal fluid (often induced by medical treatment) or to patients with insufficient tumoural response or progression. Irradiation and temozolomide are useful adjuvant therapies in a subset of patients with aggressive/invasive tumours, which are not controlled despite combined medical and surgical treatments. Because of these various challenges, we advocate a multidisciplinary management of these giant tumours in expert centres.