Unusual late development of dopamine agonist resistance in two women with hyperprolactinaemia associated with transition from micro to macroadenoma

Dopamine agonist therapy is an effective treatment in more than 90% of patients with a prolactin-secreting pituitary tumour. 1 While a minority of patients will show no response to either bromocriptine or cabergoline, the development of dopamine agonist resistance in an initially responsive prolactinoma is much more unusual. 2 We describe this phenomenon in two female patients recently under our care.