Radiographic and Hormonal Regression in Prolactinomas: An Analysis of Treatment Failure

Objective: First-line treatment for prolactin-producing pituitary adenomas is dopamine agonist (DA) therapy. This is the first study to analyze the rate of radiographic and hormonal regression of prolactinomas in response to DA therapy to better understand what time frame we consider DA treatment failure. Methods: We searched the electronic medical records of 3 tertiary care medical institutions for patients with prolactinomas. The primary outcome was tumor volume and prolactin (PRL) levels at various time points. The secondary outcome was indicators of treatment failure. Modeling by both linear and exponential models was tested to determine potential predictors of response magnitude and treatment failure by multivariate and regression analyses respectively. Results: There were 99 patients (53% male) included in this analysis. The mean patient age was 42.7 years ± 14.5, and mean width/volume of tumor at diagnosis was 12.3 mm and 1.3 cm³, respectively. The mean PRL level at diagnosis was 593.2 ng/mL (79–7913). Modeling indicated a plateau at 68.2% initial volume (95% confidence interval 61.7–73.5) by 12.6 months and a PRL plateau of 21.4 ng/mL (95% confidence interval 0–92.5) by 3.3 months. Multivariate analyses revealed male sex (odds ratio 0.168; P = 0.036) to be a predictor of faster PRL response to DA therapy. Conclusions: Prolactinomas plateau in PRL levels and the rate of size regression within the first year of DA treatment. Prolactinomas with lack of size regression and failure to reach normalization of PRL levels by 12 months may be considered for other management strategies.