Secondary Loss of Response to Dopamine Receptor Agonists in the Treatment of Macroprolactinoma.

Secondary loss of response, sometimes termed "acquired resistance," refers to the phenomenon where a patient, initially responsive to DRA therapy, as evidenced by normalized prolactin levels and/or tumor reduction, experiences a recurrence of hyperprolactinemia and/or tumor regrowth despite continued therapy at previously effective doses. This differs from primary resistance, in which patients never respond to treatment. We present an uncommonly described finding of a loss of response of macroprolactinoma treatment to cabergoline after an initial response in this case report. A literature review regarding primary and secondary resistance of prolactinomas to dopamine receptor agonist (DRA) therapy has been conducted. Patient education regarding the rare occurrence of secondary resistance of prolactinomas to DRA therapy can be better guided by this case report.