Incidental Detection With 18F-PSMA (Prostate-Specific Membrane Antigen)-1007 PET/CT of Multifocal Papillary Thyroid Carcinoma During Staging of Very High-Risk Prostate Adenocarcinoma: A Case Report

Prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) has become increasingly integrated into prostate cancer staging and restaging. PSMA expression, however, is not restricted to prostatic tissue and may be detected in several non-prostatic malignancies, including thyroid carcinoma. We report the case of a male patient with very high-risk acinar prostate adenocarcinoma (Gleason score 4+4) who underwent whole-body 18F-PSMA-1007 PET/CT for staging purposes. The patient was classified as very high-risk according to NCCN (National Comprehensive Cancer Network) criteria and was managed with androgen deprivation therapy, radiotherapy, and salvage radical prostatectomy. Imaging demonstrated a focal PSMA-avid hypodense nodule in the right thyroid lobe, measuring 15 mm with a maximum standardized uptake value (SUVmax) of 6.33. Subsequent neck ultrasonography (TI-RADS 4) and fine-needle aspiration biopsy confirmed papillary thyroid carcinoma (Bethesda category VI). The patient underwent a total thyroidectomy with a level VI central neck dissection. Histopathological examination revealed multifocal papillary thyroid carcinoma with focal vascular invasion involving three vessels and central compartment nodal metastasis (pT1bN1a). Following surgery and radioactive iodine ablation with 150 mCi of iodine-131, the patient achieved an excellent biochemical response, with thyroglobulin becoming undetectable under TSH (thyroid-stimulating hormone) suppression and no evidence of structural recurrence on follow-up imaging. This case highlights the clinical relevance of incidental focal thyroid uptake detected on PSMA PET/CT performed for prostate cancer staging. Incidental PSMA-avid thyroid lesions may occasionally identify biologically significant synchronous malignancies and should prompt dedicated evaluation with ultrasonography and fine-needle aspiration when clinically appropriate.