Giant prolactinomas: are they really different from ordinary macroprolactinomas?

Giant prolactinomas (gPRLomas) are rare tumors of the lactotroph defined by an unusually large size (>4 cm) and serum PRL levels >1000 ng/mL. The purpose of this study is to characterize the clinical spectrum of gPRLomas comparing them with non-giant prolactinomas. This is a retrospective study at a large referral center. Data from patients harboring gPRLomas and macroprolactinomas were retrieved from medical records of the Prolactinoma Clinic. Analysis was focused on clinical, biochemical, and tumor volume characteristics, as well as on the response to treatment with dopamine agonists. Among 292 patients with prolactinomas followed between 2008 and 2015, 47 (16 %) met the diagnostic criteria for gPRLomas (42 males). The most common complaint was a visual field defect; headache was reported by 79 % and sexual dysfunction was present in over half of the patients. Median basal PRL level and tumor volume were 6667 ng/mL (3750-10,000) and 32 cm(3) (20-50), respectively; hypogonadotropic hypogonadism was documented in 87 %. Cabergoline treatment resulted in the normalization of PRL levels in 68 % and in the reduction of >50 % in tumor volume in 87 % of the gPRLoma patients. The composite goal of PRL normalization and >50 % tumor reduction was achieved by 55 % (n = 26) of patients with gPRL and by 66 % (n = 100) of patients with no giant macroprolactinomas (p = 0.19). Recovery of hypogonadism and improvement of visual fields defects occurred in 32 % and 68 % of the patients, respectively. Cabergoline treatment was equally effective in patients with gPRLoma and those with macroprolactinomas in regard of achieving treatment goals, although the median CBG dose was slightly higher in the gPRLoma group (2 vs. 1.5 mg/w). Six patients required surgery. Beyond their impressive dimensions and the huge amount of PRL they secrete, the clinical behavior of gPRLoma is not different from macroprolactinomas. These tumors are highly responsive to cabergoline treatment, and pituitary surgery is seldom required.