Endocrine Abstracts

JOINT871

Introduction: Non-functioning pituitary adenomas (NFPAs) can present with hyperprolactinemia, presumably due to the pituitary stalk effect. This makes it challenging to differentiate between NFPAs and prolactinomas. In turn, this negatively affects the shared decision making process when choosing between primary dopaminergic treatment or transsphenoidal surgery. This shared decision making has increasing importance now that transsphenoidal surgery by an experienced surgeon is considered a valuable first line of treatment for prolactinomas. In the current position statement, elevated serum prolactin (PRL) levels above 250 μg/l(5.3 [IU]/L), around 11 times the upper limit of normal (ULN, set at 22 μg/l(0.47 [IU]/L)), are considered indicative of prolactinomas, whereas PRL levels of up to 150 μg/l(3.2 [IU]/l)in patients with NFPAs are attributed to the stalk effect.

Aim: To determine pretreatment cut-off values of PRL with the aim to differentiate between a prolactinoma and NFPA in patients with a radiological proven pituitary adenoma (PA) and elevated PRL.

Patients and Methods: Retrospective cohort study of patients who underwent transsphenoidal surgery between 2011 and July 2023. Inclusion criteria were 1) a histopathologically confirmed diagnosis of either a NFPA or a prolactinoma and 2) pretreatment elevated PRL levels and available pretreatment MRI. Peak PRL levels were converted to x times the local ULN to avoid standardisation differences between the used immunoassays. Diagnostic performance of peak PRL was analyzed using receiver-operating characteristics curves to calculate the area under the curve, and sensitivity and specificity. The reference standard was WHO 2017/2022 histopathological diagnosis of a (densely/sparsely granulated) lactotroph adenoma.

Pre-liminary results: Data of 80 patients (55 NFPAs and 25 prolactinomas) were analyzed. Median peak PRL levels in patients with a NFPA was 1.8 ULN (IQR 1.1, minimum 1.0, maximum 7.6). Median PRL levels in prolactinomas was 34.2 ULN (IQR 351.4, minimum 1.2, maximum 1140.0). Based on our pre-liminary results, not corrected for tumor volume, our suggested cut-off value of PRL to distinct between prolactinomas and NFPA with hyperprolactinemia ranges between 3.1 and 3.3 ULN (sensitivity range 88-92%, specificity range 80-84%).

Conclusion: Based on these preliminary results, a PRL level cut-off value of 3.1-3.3 ULN is suggested to distinct prolactinomas from NFPAs with hyperprolactinemia. This translates, based on a reference value of 22 μg/l(0.47 [IU]/L), to 68-73 μg/l(1.4-1.5 [IU]/L), substantially lower than the cutoff in the position statement. Additional analyses to evaluate the impact of tumor dimensions are ongoing.