SUN-446 Association between Prolactin Level and Tumor Size Reduction at 3 Months after Cabergoline Treatment in Patients with Macroprolactinoma

Objectives: Prolactin (PRL) normalization after 3 months of Cabergoline (CAB) treatment are useful predictors of responsiveness in patients with prolactinoma. However, differences within the PRL normalization cut-off value have not been identified. Methods: We reviewed the medical records of patients with prolactinomas who were treated with CAB as a primary drug at Severance Hospital. We included patients who had a full dataset of pituitary hormone assays and sella MRI at baseline, follow-up PRL assay and sella MRI at 3 months after CAB treatment. Results: Among the 217 patients, 123 patients had macroprolactinoma. After 3 months of CAB treatment, PRL normalization was achieved in 109 (88.6%) of macroprolactinoma patients, the mean size reduction was 22.9%. We divided these patients into two groups according to the PRL level at 3 months. When we classified by 5ng/mL, low normal group (PRL≤5, n=82) and high normal group (5<PRL≤20, n=27) did not differ in baseline PRL, tumor size and size reduction. When we classified by 1ng/mL, low normal group (PRL≤1, n=49) and high normal group (1<PRL≤20, n=60) did not differ in baseline PRL and tumor size. However, size reduction was significantly different between the two groups (27.18±18.31 vs. 19.46±13.87%, P=0.014). Even if we narrow down the high normal group (1<PRL≤10, n=50 and 1<PRL≤5, n=33), similar results came back (27.18±18.31 vs. 19.30±13.66%, P=0.017 and 27.18±18.31 vs. 19.22±14.33%, P=0.039). Conclusion: Prolactin drops to less than 1ng/ml at 3 months after CAB treatment predicts better response of macroprolactinoma.