Endocrine Abstracts

Introduction: ¹⁸F- Prostate-Specific Membrane Antigen Positron Emission Tomography/Computed Tomography (¹⁸F-PSMA PET/CT) is currently used in the evaluation of prostate cancer. Due to increased expression of PSMA in the neovascular endothelial cells of malignant lesions other than prostate cancer, PSMA PET/CT has become of interest to researchers in the management of thyroid cancer. The goal of this study was to evaluate the incidence and clinical significance of PSMA thyroid incidentaloma (PTI) detected by ¹⁸F-PSMA PET/CT scans.

Methodology: We retrospectively analyzed the clinical data of 23 patients with prostate cancer, who underwent endocrine follow-up for increased uptake in at least one focal thyroid lesion on ¹⁸F-PSMA PET/CT performed between 2018 and 2023. The indications for ¹⁸F-PSMA PET/CT were primary staging or diagnosis of biochemical recurrence after radical treatment of prostate cancer. We established our outcomes on the ¹⁸F-PSMA PET/CT reports, indications for fine needle aspiration biopsy (FNAB) according to EU-TIRADS, and cytological results according to the Bethesda Thyroid Cytology Classification. Only patients with cytological verification of PTI were included into final analysis.

Results: Data of 22 patients with 23 PTI were analyzed. The median SUVmax of PTI on ¹⁸F-PSMA PET/CT scans was 5.66 (range 2.3 - 48.39). In seven cases (31.8%), there were no indications for FNAB according to EU-TIRADS. Those patients were referred to FNAB only due to increased uptake in thyroid lesions on PSMA PET/CT. The results of FNAB were as follows: 19 (82.6%) benign; 2 (8.7%) atypia of undetermined significance; 1 (4.3%) follicular neoplasm; 1 (4.3%) malignant. The only malignant lesion was diagnosed as papillary thyroid cancer on cytology. The SUVmax of corresponding lesion on PSMA PET/CT was 3.6, and US revealed no indications for FNAB with EU-TIRADS 4 and size of the lesion of 8 mm. Due to the low stage of the tumor, this patient remains on active surveillance. Any other lesion that was subjected to further follow-up [median 5 months (0-42)] did not become clinically significant.

Conclusions: ¹⁸F-PSMA PET/CT seems not to be a useful modality for the differentiation of benign and malignant thyroid lesions. Standard methods of evaluating thyroid nodules are sufficient for further diagnosis of PTI, without the need to verify all lesions on FNAB. The only detected thyroid cancer in our study was a lesion with an indolent course. Further research on larger cohort is necessary to explore the role of PSMA PET/CT in management of thyroid nodules.