We present a unique case of a solitary retroperitoneal metastasis from follicular thyroid carcinoma (FTC), incidentally detected by a staging [18F]-prostate-specific membrane antigen (PSMA)-1007-positron emission tomography (PET)-computed tomography (CT) for prostate cancer (PCa) and confirmed by subsequent investigations. This evidence concerns the gene FOLH1 and Familial prostate cancer.