Shrinkage by the third month predicts long-term response of macroprolactinoma after cabergoline.

Objective Transsphenoidal surgery (TSS) is mainly indicated in prolactinomas when dopamine agonist treatment fails. However, there is no established early predictor of cabergoline (CBG) response. The present study was aimed to identify predictors of CBG resistance in order to select patients who may benefit from early TSS. Design Retrospective longitudinal study. Methods We reviewed the medical record of patients diagnosed with prolactinoma after 2010. Inclusion criteria: macroprolactinomas under CBG treatment with serial prolactin levels and MRI before treatment and 3 and 12 months afterwards. The main outcome was tumour size shrinkage ≥ 50% (using the two largest diameters in sagittal view) after 12 months of CBG (TS_50). The capacity of the most important clinical and biochemical variables in predicting the main outcome was examined. Results A total of 185 prolactinomas where included: 124 (67.0%) were microadenomas and 61 (33.0%) were macroadenomas of which 27 patients meet de inclusion criteria; median age (42.5 years; (IQR: 28.0)). The median follow-up was (67.5 months; (IQR: 30.2)). Ten patients (37.0%) underwent surgery after more than 1 year of CBG. The volume reduction at the first MRI (3-4 months) was the unique valuable predictor: (OR: 1.16 (95% CI: 1.02-1.32)) of TS_50. A tumour volume shrinkage of ≥ 30% in the first 3-4 months of CBG therapy predicts TS_50 with an AUC (0.95 (CI: 0.76-0.99)). Conclusion Tumour shrinkage in the first 3-4 months after starting treatment with CBG is a good tool for predicting the long-term response and can help clinicians to take more appropriated and personalized decisions.