LATE DEVELOPMENT OF RESISTANCE TO BROMOCRIPTINE IN A PATIENT WITH MACROPROLACTINOMA

We report the case of a man with an invasive macroprolactinoma who dev eloped resistance to bromocriptine to which he had previously responde d satisfactorily for 5 years. Subsequently, hyperprolactinemia was con trolled equally well with 600 mu g quinagolide daily and later with 4. 5 mg cabergoline weekly. This observation suggests that a loss of dopa mine receptors at the tumoral cell surface might be the mechanism unde rlying acquired resistance to bromocriptine. In addition, no tumor gro wth was observed over a 10-year follow-up, which virtually excludes a malignant transformation of the prolactinoma. This case emphasizes the need for close supervision of patients with macroprolactinoma, even a fter the serum prolactin concentration has been normalized by bromocri ptine. It furthermore illustrates the usefulness of quinagolide and ca bergoline when resistance to bromocriptine develops after a prolonged period of adequate response to this drug.