Cabergoline Therapy and Tumor Growth Rate in Pituitary Microadenomas: A Retrospective Cohort Study

Objective: To compare tumor growth rate between patients with pituitary microadenomas who had mild to moderate prolactin elevation and symptoms leading to initiation of cabergoline therapy, and asymptomatic microadenomas without prolactin elevation managed with observation. Materials and Methods: In this retrospective cohort study, 139 patients diagnosed with pituitary microadenoma between 2019 and 2024 and with at least 12 months of clinical and radiological follow-up were included. Patients who received cabergoline therapy due to symptoms were classified as the dopamine agonist-positive [DA(+)] group, while those who did not receive treatment were classified as the dopamine agonist-negative [DA(-)] group. Tumor growth rate was calculated as the annual change (mm/year) in maximum tumor diameter on serial magnetic resonance imaging. Between-group comparisons were performed using the Mann-Whitney U test. A mixed-effects linear model was constructed to evaluate the interaction between time and treatment. Results: Of the 139 patients included in the study, 42 were in the DA(+) group and 97 were in the DA(-) group. There were no significant differences between the groups in terms of baseline age, follow-up duration, or tumor size (p > 0.05). The mean tumor growth rate was 0.67 ± 0.80 mm/year in the DA(-) group and 0.36 ± 0.38 mm/year in the DA(+) group (p = 0.0208). In the mixed-effects model analysis, the time × treatment interaction was statistically significant (β = -0.021 mm/month; p = 0.009). Patients receiving cabergoline showed a marked reduction in prolactin levels and improvement in symptoms in 78% of cases. Importantly, no tumor shrinkage was observed in either group; the primary observed effect was a reduction in growth velocity rather than true tumor regression. No serious treatment-related adverse effects were observed. Conclusions: In patients with pituitary microadenomas, cabergoline therapy was associated with a reduced tumor growth rate over time, while no true tumor regression was observed. These findings suggest that cabergoline exposure may influence longitudinal tumor growth dynamics in clinically ambiguous cases encountered in routine practice, without implying definitive tumor subtype classification.