Shrinkage of a PRL-secreting pituitary macroadenoma resistant to cabergoline

Abstract

Cabergoline decreases both serum PRL levels and size of prolactinomas, including some tumors resistant to other dopamine-agonists. It is common observation that the shrinkage of the adenoma is preceded by suppression of PRL levels. A minority of patients, who do not show a significant decrease of PRL after a short trial with dopamine-agonists, undergoes neurosurgery or radiotherapy. We report on the case of a 14-year-old girl with a huge prolactinoma who showed, during cabergoline treatment (0.5 mg twice a week), a significant shrinkage of the pituitary mass but no decrease of the very high PRL values. She was referred to us after partial removal of the suprasellar extension of the pituitary tumor. The post-surgical evaluation showed very high PRL levels (9352 μg/l; 20941 μg/l before surgery), which did not decrease during the 2-year treatment with cabergoline (nadir value: 8735 μg/l). However, one month after the beginning of therapy, MRI showed a significant shrinkage of the tumor (tumor volume 5.7 ml, compared with 45.1 ml prior to surgery and 24.4 ml after surgery). Subsequently MRIs demon-strated a progressive reduction of the size with a complete disappearance of the suprasellar and parasellar tissue (tumor volume 1.8, 0.9 and 0.2 ml, at 3, 6 and 12 months, respectively). The MRI performed at the 24^th month showed a secondary empty sella, with residual tumor tissue in the right sphenoidal sinus. Increasing cabergoline, up to 3 mg a week, failed to induce any decrease of PRL levels. In conclusion, in such macroprolactinomas the shrinkage of tumor is not strictly correlated with (or it is partially dissociated from) the inhibition of PRL hypersecretion. The choice of other therapeutic options in cabergoline-resistant macroprolacti-nomas needs careful neuroradiological evaluation after a short trial of pharmacological treatment.