[Development of secondary resistance to dopamine agonists in a patient with giant prolactinoma].

Currently conservative treatment is therapy of choice in most patients with prolactinoma. However in 10-20% of them resistance to dopamine agonists occurs. In the majority of such cases resistance is initial, and only a few patients after good primary response to dopamine agonists develop so called "secondary" resistance ("escape" from effect). Alternative method of treatment in this situation is surgery, but in case of large invasive adenoma radical removal is often not possible. Consequently, radiation therapy may be feasible. Among 306 patients with macroadenomas examined in Burdenko Neurosurgical Institute (Moscow, Russia) only 2 (0.65%) developed "secondary" resistance to dopamine. In 1 case radiation therapy allowed effective control of tumor size and decrease of prolactin level. 1 case is described in details, and histological material was analyzed meticulously. Downregulation of D2R receptors in tumor cells may be one of the possible mechanisms of resistance to dopamine agonists.