Resistant prolactinomas: a case series of 26 patients

Prolactin (PRL)-secreting tumors are the most common functional pituitary adenomas. They usually respond to dopamine agonist (DA) treatment, with PRL normalization and adenoma shrinkage. Our aim was to characterize patients with prolactinoma resistant to DA treatment.

This retrospective case series included patients diagnosed with DA-resistant prolactinomas between 1993-2017 in three medical centers. Resistance was defined as PRL levels above three times the upper limit of normal (ULN) despite a weekly dose of ≥2 mg cabergoline (CAB). Clinical and biochemical information, and response to treatment, were retrieved from medical records.

Twenty-six patients were identified; 20 males. Of 25 macroadenomas, three were giant tumors (>40 mm) and 15 (57.7%) were invasive. The mean age at diagnosis was 31.8 ± 14.9 years (range: 13-62). The median maximal CAB dose was 3.5 mg/week (IQR, 2.5-5). Half the patients received only CAB in escalating doses, nine received CAB and underwent transsphenoidal surgery, and four underwent surgery and radiotherapy in addition to CAB treatment. PRL levels at baseline between patients treated only with CAB and those operated were (91.6 [51.1-296.7] vs. 73.1 [22.6-170.9] XULN p = 0.355), and under maximal CAB dose PRL levels between patients treated only with CAB and those operated were similar (5.77 [1.27-11.27] vs 5.27 (2.9-26) XULN p = 0.317). At the last visit patients who received combined therapy achieved lower PRL levels than those treated with DA only (5.22 [1.7-21.6] vs 1.1 [0.44-3.99] XULN p = 0.017) PRL normalization was attained in seven patients and levels below 3 × ULN in fourteen patients; the overall response was 56%.

Resistant prolactinomas usually require a multi-modal treatment strategy. We were able to control 14/25 (56%) of resistant tumors.