Endocrine Abstracts

About 10–15% of prolactinomas (P) are resistant to Dopamine agonists (DA). We analyzed retrospectively ten resistant prolactinomas (RP) treated at our center between 1995 and 2014, to identify useful variables to predict DA resistance and its different patterns (biochemical resistance (BR), morphological resistance (MR) or both). BR is defined as the failure to normalize prolactin (PRL) levels with ≥ 2 mg/week of cabergoline (C) for at least 3 months. MR is considered when at that dose the tumor size is not reduced by at least 50%. The median age was 30.6 years and 5 subjects were male. All patients had secondary hypogonadism and 1 had TSH and GH deficiency. The median PRL levels were 548 (127–1000) ng/ml. There were eight macroprolactinomas (MP) and two microprolactinomas (mP), with an average size of 1.78 (0.4–3.5) cm. Seven had suprasellar extension and three invasion of cavernous sinuses. The median dose of C used was 3.4 (2–7) mg/week. The median follow-up was 93.2 (26–348) months. Five patients had MR, 1 BR and 4 patients both. Seven patients (2 mP and 5 MP) underwent transsphenoidal surgery. The indication was BR and MR in 4, BR in 1 and MR in the other 2 patients. The surgical remission was achieved in 3 patients. The remaining 4 patients were treated with DA and one of them also received radiotherapy. All of them achieved remission. In the 3 non-operated patients an adequate hormonal control was achieved, but with tumor persistence. In conclusion, prevalence of male sex, a size larger than 1 cm and suprasellar extension were higher in our resistant patients than that reported in non-resistant prolactinomas; thus, these features could predict DA resistence. The morphological response without biochemical response is uncommon, whereas MR without BR is relatively frequent, even more than the coexistence of both.