Short-term decline in prolactin concentrations can predict future prolactin normalization, tumor shrinkage, and time to remission in men with macroprolactinomas

Objective: To identify early follow-up measures that will predict the dynamics of prolactin (PRL) decrease and adenoma shrinkage in men harboring macroprolactinomas. Methods: A single-center historical prospective study including a consecutive group of 71 men with pituitary macroadenomas (≥10 mm) and hyperprolactinemia (PRL >7 times the upper limit of normal [ULN] treated medically with cabergoline. Comparisons of PRL normalization rates were performed according to PRL levels achieved at 6 months, maximal adenoma shrinkage during follow-up, and other patient characteristics. Correlations were analyzed to identify characteristics of PRL suppression dynamics. Results: PRL levels after 6 months of treatment correlated positively with current PRL levels (r = 0.74; P<.001), with time to PRL normalization (r = 0.75; P<.001), and with adenoma diameter following treatment (r = 0.38; P =.01). Adenoma shrinkage depicted by first magnetic resonance imaging on treatment correlated with maximal adenoma shrinkage during follow-up (r = 0.56; P =.006). Five patients had nadir PRL levels ≥3 times the ULN (51 ng/mL) and showed slower response to cabergoline treatment, with consistently higher PRL levels compared with responding patients throughout follow-up (mean 6-month PRL levels, 519 ± 403 ng/mL versus 59 ± 118 ng/mL; P<.001). Conclusion: Six-month PRL level might serve as a surrogate marker for PRL normalization and adenoma shrinkage dynamics among men harboring macroprolactinomas.