SERUM PROLACTIN TO TUMOR SIZE RATIO AS AN EFFECTIVE PARAMETER TO ACCURATELY DISTINGUISH PROLACTINOMA FROM NON FUNCTIONING PITUITARY TUMOR: A JOURNAL-STYLE ORIGINAL RESEARCH DRAFT

Abstract

Background: Distinguishing prolactinoma from non-functioning pituitary tumor (NFPT) in patients with sellar lesions and hyperprolactinemia is essential because first-line treatment differs substantially between the two entities. Absolute serum prolactin is helpful but may be misleading in the presence of stalk effect. Aim: To evaluate whether the serum prolactin to tumor size ratio improves diagnostic discrimination between prolactinoma and NFPT. Methods: This journal-style observational diagnostic study included 75 untreated adults with hyperprolactinemic sellar lesions, comprising 39 prolactinomas and 36 NFPTs. Clinical profile, magnetic resonance imaging characteristics, serum prolactin, prolactin/maximum diameter ratio, and prolactin/tumor volume ratio were analyzed. Receiver operating characteristic analysis was performed to determine optimal cutoffs and diagnostic performance. Results: Patients with prolactinoma were younger and more often female, and they had more galactorrhea and hypogonadism, whereas NFPTs were larger and more frequently associated with visual field defect, hypopituitarism, and stalk deviation. Median serum prolactin was 198.53 ng/mL in prolactinoma versus 74.05 ng/mL in NFPT (p<0.001). Median prolactin/maximum diameter ratio was 19.17 versus 4.24 ng/mL/mm, respectively (p<0.001). Serum prolactin correlated with tumor size in prolactinoma but not in NFPT. On ROC analysis, prolactin/maximum diameter ratio showed the highest diagnostic performance (AUC 0.995, 95% CI 0.983-1.000) with an optimal cutoff of 11.03 ng/mL/mm, sensitivity 94.9%, specificity 100%, and accuracy 97.3%. Conclusion: The serum prolactin to tumor size ratio, particularly prolactin divided by maximum tumor diameter, is a practical and highly accurate adjunct for differentiating prolactinoma from NFPT. Incorporating tumor size into prolactin interpretation may improve preoperative triage and reduce inappropriate initial management.