Clinical Significance of incidental findings of thyroid nodules with increased PSMA-uptake on PET

High uptake on PSMA PET has been reported for several solid non-prostate cancers, including thyroid carcinoma. PSMA uptake in benign thyroid nodules has been reported as well. In this retrospective single institution study, we investigated the incidence and etiology of incidentally detected thyroid nodules with uptake on PSMA PET in a cohort of prostate cancer patients.

We performed a search of our imaging database and identified PSMA PET demonstrating focal thyroid uptake. When multiple PSMA PET, only the first that demonstrated a thyroid nodule with PSMA-uptake was included. PET images were reviewed visually and by measuring the maximum standardized uptake value (SUVmax) of the focal thyroid uptake. Ultrasound images, TI-RADS scores, cytology (Bethesda grade) and surgical pathology reports were reviewed.

110 patients with focal thyroid PSMA-uptake who subsequently underwent ultrasound were included. Five had normal thyroid ultrasound. Five demonstrated two foci. FNAC was performed for 71 nodules in 68 patients. Cytology was nondiagnostic in 3 (4.2%; Bethesda I), benign in 37 (52.1%; Bethesda II), atypia of undetermined significance in 11 (15.5%; Bethesda III), suspicious for follicular or oxyphilic neoplasm in 8 (11.3%; Bethesda IV), suspicious for malignancy in 2 (2.8%; Bethesda V), and malignant in 10 (14.1%; Bethesda VI). A total of 15 malignancies were identified.

In our cohort of prostate cancer patients, thyroid nodules with PSMA-uptake incidentally found on PET were primary thyroid carcinoma in 13.6%. An incidental finding of a thyroid nodule with PSMA-uptake should be considered for further follow up with ultrasound and FNAC.