# The clinical value of [18F]-fluoro-ethyl-L-tyrosine PET ([18F]FET-PET) correlated with MRI in patients with functioning pituitary adenomas: an observational cohort study

## TL;DR

[18F]FET-PET improves detection of pituitary tumors when MRI results are unclear, helping guide treatment decisions.

## Contribution

Demonstrates [18F]FET-PET's clinical utility in detecting functioning pituitary adenomas with negative or equivocal MRIs.

## Key findings

- [18F]FET-PET detected lesions in 76% of scans, with high sensitivity (86%) and positive predictive value (71%).
- It localized tumors in patients with acromegaly despite ongoing treatment, showing potential for personalized care.
- Results were often discordant with MRI, suggesting complementary diagnostic value.

## Abstract

To assess the clinical value of [18F]fluoroethyl-L-tyrosine PET ([18F]FET-PET) correlated with MRI in patients with functioning pituitary adenoma (FPA) with negative or equivocal conventional MRIs during diagnosis, persistent disease and recurrence.

Retrospective observational cohort study of 34 patients with FPAs who underwent a total of 37 [18F]FET-PETs (Cushing’s disease: n = 19, acromegaly: n = 14, prolactinoma: n = 3, and TSH producing adenoma: n = 1) between January 2022 and April 2025. The clinical performance was assessed in the surgically treated cohort, using confirmative histopathology and/or postoperative remission as reference standard.

[18F]FET-PET identified a single lesion in 28 scans (76%), two lesions in 1 scan (3%), and no lesion in 8 scans (22%). [18F]FET-PET and MRI were concordant positive in 14/37 scans, concordant negative in 1/37, discordant MRI+/[18F]FET-PET + different location in 2/37, discordant MRI-/[18F]FET-PET + in 8/37, discordant MRI+/[18F]FET-PET- in 7/37 and partly concordant in 5/37 scans. In 14 cases surgery resulted in confirmative histopathology and/or postoperative remission, 12 of those had a positive [18F]FET-PET. In 6 cases surgery did not result in confirmative histopathology and/or postoperative remission, of whom 5 had a positive [18F]FET-PET. Overall, the sensitivity was 86% and the positive predictive value 71%. In three patients with acromegaly, [18F]FET-PET was able to localize a lesion, despite biochemical control under continued somatostatin analogue treatment.

[18F]FET-PET enhances lesion detection and improves personalized treatment in patients with FPA and negative or equivocal conventional MRIs throughout the disease course. Consensus on the timing of [18F]FET-PET with respect to medication and biochemical status is warranted.

The online version contains supplementary material available at 10.1007/s11102-025-01634-w.