Introduction: Dopamine agonists are the mainstay treatment for prolactinomas, but clinical characteristics that predict their effects on prolactin (PRL) suppression and tumour shrinkage are missing. Our study aimed to find measures in early follow-up of men harbouring macroprolactinomas, that will predict dynamics of PRL decrease and adenoma shrinkage.
Methods: A single centre historical prospective study, including a consecutive group of 71 men with pituitary macroadenomas (≥10 mm) and hyperporlactinaemia (>7xULN), treated medically with cabergoline. Comparisons of PRL normalisation rates were performed according to PRL levels achieved at 6 months, maximal adenoma shrinkage during follow-up, and other patient characteristics. Correlations were performed to identify characteristics of PRL suppression dynamics.
Results: Five patients had nadir PRL levels ≥x 3 ULN (51 ng/ml), and showed slower response to treatment with cabergoline with consistently higher PRL levels compared to other patients throughout follow-up (6 months mean PRL levels, 519±403 vs. 59±118 ng/ml, P<0.001). PRL levels after 6 months of treatment correlated positively with current PRL levels (r=0.74, P<0.001), with adenoma diameter following treatment (r=0.38, P=0.01), and with time to PRL normalisation (r=0.75, P<0.001). Shrinkage of adenoma size depicted by first MRI on treatment correlated with maximal adenoma shrinkage during follow-up (r=0.56, P=0.006).
Conclusions: Six months PRL level might serve as a surrogate marker for PRL normalization and adenoma shrinkage dynamics among men harbouring macroprolactinomas. Among these patients with persistent hyperprolactinaemia at 6 months, higher PRL levels are associated with resistance to cabergoline.