PSMA PET/CT Incidental Detection of Tumor Thrombus From Unsuspected Renal Cell Carcinoma and Comparison with FDG PET/CT

Clear cell renal cell carcinoma (ccRCC) is typically prostate-specific membrane antigen (PSMA)-avid, likely related to PSMA expression in the tumor neovasculature, suggesting a potential role for evaluation by PSMA PET/CT. We describe a 77-year-old patient with prostate cancer who was incidentally found to have ccRCC on imaging with PSMA PET/CT, with subsequent staging by FDG PET/CT. He was diagnosed with prostate cancer 17 years prior and treated with radical prostatectomy and radiation therapy within a year of diagnosis. Biochemical recurrence with PSA of 1.0 ng/mL prompted imaging with PSMA PET/CT, which showed an unexpected finding of abnormal uptake within the right renal vein and inferior vena cava (IVC), suggesting possible tumor thrombus (SUVmax 8.8), with mild uptake corresponding to a suspected right renal mass. In addition, there was a PSMA-avid right paratracheal nodal metastasis measuring 3.3 cm (SUVmax 8.4). Subsequent FDG PET/CT again showed the renal mass, tumor thrombus (SUVmax 3.6), and only low-level uptake in the right paratracheal mass (SUVmax 2.3). Right nephrectomy was performed, confirming the presence of ccRCC in the right kidney with tumor thrombus extending to the right renal vein and IVC. FDG PET/CT restaging showed no recurrence in the nephrectomy bed and a stable FDG-avid right paratracheal mass. After stereotactic body radiation therapy (SBRT) directed to the right paratracheal mass, follow-up PSMA PET/CT showed decreased uptake (SUVmax 4.8), suggesting its usefulness for detecting and monitoring ccRCC.