Effectiveness of short-term maintenance treatment with cabergoline in microadenoma-related and idiopathic hyperprolactinemia
Pituitary adenomas occur with an estimated prevalence of 17%, with prolactinomas being the most frequent of the hormone-secreting tumors.1 Microprolactinomas are less than 1 cm in dia meter and are more common in women than men, whereas macroprolactinomas are larger and cause spatial effects, including compression of the optic apparatus. The goal of therapy is to restore gonadal function in both types of prolactinoma and to decrease tumor volume in macro prolactinoma. Medical inter vention uses dopamine agonists, which act by stimulating D2 dopamine receptors. In the majority of cases there is a good response to these drugs, both in terms of normalizing prolactin levels and decreasing tumor size, although these effects do not necessarily occur simultaneously. Dopamine-agonist resistance can occur in some prolactinomas, however, probably because of a low expression level of tumor-associated D2 receptors.2 In this class of drugs, resistance occurs least frequently with cabergoline, making it the drug of choice for treating prolactinoma.2 Around 85% of patients achieve a normal prolactin level after 6 months of cabergoline treatment and doses of caber goline of up to 7 mg per week have been reported, although the long-term safety of such doses has not been tested. The mechanism of action of dopamine agonists in tumor shrinkage and the lowering of prolactin levels is complex. These drugs initially reduce both the number and size of intracellular prolactin secretory granules, suggesting a role in inhibiting prolactin release. Overall, there is a reduction in the size of the lactotroph adenoma cells because of regression of the rough endoplasmic reticulum and Golgi apparatus, which is associated with cessation of intracellular prolactin synthesis. Chronic dopamine-agonist administra tion also has a cytocidal effect.3 Early studies showed that macroprolactinomas could rapidly re-expand following dopamine agonist withdrawal.4,5 This observation was occasionally exploited therapeutically in patients When to discontinue treatment of prolactinoma?