Endocrine Abstracts

Introduction: Dopamine agonists, mainly cabergoline and bromocriptine, represent the first-line treatment option in the management of prolactinomas. They allow prolactin normalization and tumor shrinkage. However, a subset of individuals with macroprolactinoma could exhibit a varying degree of resistance to dopamine agonists. The aim of this study was to determine the prevalence of dopamine agonist-resistance in patients with macroprolactinoma and to assess its predictive factors.

Methods: This was a single-center, retrospective study including 52 patients with macroprolactinoma. All enrolled patients were treated with dopamine agonists (cabergoline or bromocriptine). Resistance to dopamine agonists was defined as failure to achieve normoprolactinemia and/or 30% tumor shrinkage. Age, gender, epidemiological parameters, medical history, and clinical and paraclinical data were collected from medical records.

Results: Twenty-seven men and 25 women were enrolled in this study. Their mean age at the diagnosis of macroprolactinoma was 34.7 ± 14.9 years. The median baseline prolactin level was 1879 µg/l. The mean baseline macroprolactinoma size was 35 ± 17 mm (extremes: 11-77 mm). Macroprolactinoma was invasive in 73% of cases, with hemorrhagic or necrotic components in 52% of cases. Dopamine agonist resistance was observed in 16 patients (31%). Univariate analysis showed that age at diagnosis <30 years (OR=5, 95%-confidence interval (95%-CI):1.13-14.29, P=0.011), baseline prolactin level > 7000 µg/l (O r=4.86, 95%-CI:1.14-20.63, P=0.035), invasive adenoma (OR=10.26, 95%-CI: 1.20-87.55, P=0.018), presence of hemorrhagic or necrotic components (OR=28.5, 95%-CI: 3.27-248.17, P=10^-3), and tumor size > 40 mm (OR=7, 95%-CI: 1.71-28.54, P=0.004) were associated with dopamine agonist-resistance. In multivariate analysis, the presence of hemorrhagic or necrotic components was the only independent predictor of dopamine agonist-resistance (adjusted-O r=28.68, P=0.005).

Conclusion: Dopamine agonist-resistance was frequent in patients with macroprolactinoma. Its predictive factors included young age, invasive tumor, high baseline prolactin levels, tumor size, and the presence of hemorrhagic or necrotic components. The latter was the only independent predictor of treatment resistance.