EPID-13. PREDICTIVE VALUE OF SERUM PROLACTIN LEVEL TO THE TUMOR SIZE RATIO FOR PREOPERATIVE DIAGNOSIS OF PROLACTIN-PRODUCING PITUITARY ADENOMA

Abstract

Abstract PURPOSE Preoperative diagnosis of prolactinomas is critical because medication of dopamine agonists instead of surgical resection has been regarded as a primary treatment. However, serum prolactin level alone is suboptimal for differentiating the prolactin producing adenoma or hyperprolactinemia-causing NFPAs. The author investigated the use of ratio of PRL levels to the tumor size as the optimal cutoff value for prolactin-producing tumor, comparing with the NFPA. METHOD We performed a retrospective review of patients who underwent the transsphenoidal surgery (TSS) for pituitary lesions in the single institute between January 2015 to May 2020. A total of 223 patients with hyperprolactinemia at the initial diagnosis were analyzed in the study, including NFPA patients (n=175) and prolactinoma patients (n=48). Receiver operating curve (ROC) analyses were performed for serum prolactin levels (PRL) and serum prolactin levels/tumor maximal diameter (PRL/MD). RESULT Prolactinoma group showed higher median values in serum PRL (258.6 μg/L) and smaller maximal tumor diameter (16.6 mm), compared to those of NFPA group (serum PRL 44.4 μg/L, p-value = 0.002 and MD 23.9 mm, p-value < 0.001). A moderate correlation was found between serum prolactin level and maximal diameters in prolactinomas (r=0.43, p=0.002), whereas a weak relationship was confirmed in NFPAs (r=0.17, p=0.028). The cutoff was 8.93 μg/L*mm (area under the curve [AUC] = 0.94) for PRL/MD and 99.43 μg/L for PRL (AUC = 0.91). In prolactinomas, there was no statistical difference between the PRL/MD of macroadenomas (n=36, 21.7μg/L*mm) and microadenoma (n=12, 16.8μg/L*mm) (p=0.109). CONCLUSION The serum PRL levels and tumor size exhibited stronger linear correlation in prolactinomas than in NFPAs. The PRL/MD ratio showed better diagnostic value for differentiating two pathologies than the serum PRL levels alone. These findings suggest PRL/MD ratio may be an alternative method to preoperative diagnosis of prolactinomas differentiating from hyperprolactinemia-causing NFPAs.