SAT-127 - Microprolactinomas: Correlations between Tumor Size, Prolactin Levels, and Treatment Response

Background:
Microprolactinomas are benign pituitary adenomas characterized by hyperprolactinemia and hypogonadal symptoms. They come in varying sizes and treatment uses dopamine agonists, particularly cabergoline. Although treatment often results in prolactin reduction and tumor shrinkage, responses differ across patients, and the factors influencing these differences remain unclear.

Objective:
To evaluate relationships between baseline tumor size, prolactin (PRL) levels, and treatment response in patients with prolactinomas treated with cabergoline.

Methods:
This retrospective observational study used electronic medical record data from a large endocrinology and psychiatry practice from 2017–2025. Patients with prolactin-secreting pituitary adenomas treated with medication were included. Data collected included baseline and follow-up serum prolactin levels, tumor size(s) on MRI, treatment duration, and time to biochemical recurrence after medication discontinuation. Pearson correlation analyses were performed, with significance defined as p < 0.05.

Results:
Seventy-five patients were included (63 females [84%], 12 males [16%]; mean age 40.76 years). Tumor shrinkage rate was moderately positively correlated with baseline tumor size (r = 0.48, p = 0.002), strengthening after exclusion of outliers (r = 0.55, p = 0.001). Baseline tumor size was also positively correlated with prolactin reduction rate (r = 0.61, p = 0.005). Prolactin reduction rate after starting medication strongly correlated with total prolactin reduction (r = 0.95, p < 2.2 × 10⁻¹⁶), remaining significant after outlier exclusion (r = 0.62, p = 1.13 × 10⁻⁶). Baseline tumor size and prolactin levels demonstrated a moderate positive correlation (r = 0.63, p = 9.61 × 10⁻⁸). Among patients who discontinued therapy, median time to biochemical recurrence was 7.0 months.

Conclusion:
This study demonstrates correlations between tumor size, prolactin levels, and treatment response in patients with prolactinomas treated with cabergoline. Larger baseline tumor size was associated with greater tumor shrinkage and faster prolactin reduction, while higher baseline prolactin levels were linked to greater overall prolactin decreases, further characterizing treatment response patterns in prolactinoma management. Limitations include variable imaging, the influence of outliers, as well as the single-practice setting, which may limit generalizability. Despite these limitations, by examining relationships between tumor size, prolactin levels, and reduction rates, the study helps further characterize the course of microprolactinomas under medical management.

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