Inconsistent Detection of Sites of Metastatic Non-Clear Cell Renal Cell Carcinoma with PSMA-Targeted [18F]DCFPyL PET/CT

To investigate the utility of prostate-specific membrane antigen (PSMA)-targeted [18F]DCFPyL positron emission tomography (PET)/X-ray computed tomography (CT) imaging for the detection of sites of disease in patients with metastatic non-clear cell renal cell carcinoma (RCC). Eight patients with metastatic non-clear cell RCC underwent imaging with PSMA-targeted [18F]DCFPyL PET/CT. Imaged RCC histologic subtypes included papillary RCC (n = 3), chromophobe RCC (n = 2), unclassified RCC (n = 2), and Xp11 translocation RCC (n = 1). Using comparison to conventional CT and/or magnetic resonance imaging as reference, two radiologists with expertise in nuclear medicine identified putative sites of disease on [18F]DCFPyL PET/CT and classified each lesion as having no radiotracer uptake, equivocal uptake, or definitive uptake. In total, 73 metastatic sites and 3 primary tumors compatible with sites of non-clear cell RCC were identified on conventional imaging. Metastatic sites of disease included lymph nodes (n = 40), venous thrombi (n = 3), pulmonary nodules (n = 10), bone lesions (n = 15), brain lesions (n = 3), and retroperitoneal masses (n = 2). Only 10 of the 73 lesions (13.7 %) were classified as having definitive radiotracer uptake (median SUVmax = 3.25, range = 1.2–9.5), 14 lesions (19.2 %) had equivocal uptake (median SUVmax = 2.85, range = 0.5–6.5), and 49 lesions (67.1 %) had no definitive uptake above background (median SUVmax = 1.7, range = 0.2–3.0). The three primary renal tumors demonstrated lower radiotracer avidity relative to surrounding normal renal parenchyma. A small proportion of sites of non-clear cell RCC showed uptake of the PSMA-targeted radiotracer [18F]DCFPyL. Unlike for clear cell RCC, the results of this study indicate that PSMA-based PET is not appropriate for imaging other RCC subtypes.