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Neuroendocrinology and Pituitary

MON-119 - Prolactin Levels, but Not T2-Weighted Tumor Signal, Discriminated between Non-Functioning Pitnets and Lactotroph Pitnets

Monday, June 15, 2026
9:00 AM - 2:00 PM CT
Location: ENDOExpo; Poster Floor


Introduction: Both prolactin-secreting PitNETs (PRL-PitNETs) and non-functioning PitNETs (NF-PitNETs) can cause different grades of hyperprolactinemia, the first ones by directly producing it, the other ones by compression of the pituitary stalk. This study aimed to investigate the usefulness of biochemical and radiological features in differentiating between non-functioning PitNETs and secreting lactotroph Pit-NETs.

Patients and methods: 166 patients with clinical suspicion of NF-PitNET or PRL-PitNET and histological confirmation were included in the study. For all patients were collected prolactin levels at diagnosis, tumor volume and consistency, ratio between MRI-based T2-weighted tumor signal and T2-weighted white matter intensity.

Results: 143 NF-PitNETs and 23 PRL-PitNETs were included in the study. 16 cases were microPitNETs (8 NF-PitNETs, 8 PRL-PitNETs) and 150 were macro-PitNETs (135 NF-PitNETs, 15 PRL-PitNETs). Tumor consistency was cystic in 47 cases (39 NF-PitNETs, 8 PRL-PitNETs) and solid in 119 cases (104 NF-PitNETs; 15 PRL-PitNETs). As T2-ratio significantly differed between cystic and solid PitNETs (p < 0.001), we separately analyzed the two groups. Among cystic PitNETs, T2-ratio didn’t differ in NF-PitNETs and PRL-PitNETs, both micro- (p=0.2) and macro-PitNETs (p=0.248); instead, prolactin levels were significantly higher in PRL-PitNETs than in NF-PitNETs, both micro- (respectively, 500 ng/mL SD: 125 and 28.7 ng/mL SD: 25 p< 0.001) and macro-PitNETs (respectively, 428 ng/mL SD: 321 and 28.2 ng/mL SD: 25 p< 0.001). Likewise, among solid PitNETs, T2-ratio didn’t differ in NF-PitNETs and PRL-PitNETs, both micro- (p=0.977) and macro-PitNETs (p=0.243); instead, prolactin levels were significantly higher in PRL-PitNETs than in NF-PitNETs, both micro- (respectively 162 ng/mL SD: 91 and 21 ng/mL SD: 24 p=0.003) and macro-PitNETs (respectively 195 ng/mL SD: 428 and 20 ng/mL SD: 193 p< 0.001).

Discussion: In this study, serum prolactin levels confirmed their reliability as a biochemical marker in distinguishing PRL-PitNETs from NF-PitNETs, independently of tumor size or consistency. Conversely, MRI-based T2-weighted signal ratios didn’t help differentiate the secretory status, highlighting the limited diagnostic role of conventional MRI features. Advanced MRI modalities (such as radiomics, DWI, susceptibility imaging, and molecular imaging) could further improve diagnostic accuracy by providing quantitative, microstructural, and functional data beyond standard imaging and serum prolactin levels.

Conclusion: Prolactin levels at diagnosis, but not T2-weighted tumor signal, predict the diagnosis of secreting lactotroph tumors rather than non-functioning PitNETs.

*Unless otherwise noted, all abstracts presented at ENDO must not be released to the press or the public until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.*