Figure 2.

Large lytic lesions were present in the posterior aspects of both iliac bones in this patient, and both sites were found to have intense uptake of both radiotracers (¹⁸F-FDG in A and B and ¹⁸F-DCFPyL in C and D, red arrowheads). However, ¹⁸F-DCFPyL uptake was both visually and quantitatively higher than ¹⁸F-FDG. For the right iliac lesion, ¹⁸F-FDG uptake yielded SUV_max of 3.3, while for the same lesion ¹⁸F-DCFPyL uptake generated SUV_max of 16.6. For the left iliac, ¹⁸F-FDG SUV_max was 4.0 while ¹⁸F-DCFPyL SUV_max was 13.9. In aggregate, our findings in this patient with metastatic clear cell RCC are suggestive that ¹⁸F-DCFPyL may able to identify more lesions and has higher tumor uptake than ¹⁸F-FDG. Although a significant body of work has examined the role of ¹⁸F-DCFPyL and other small molecule inhibitors targeted against PSMA in the detection of prostate cancer [1-4], the use of such radiotracers for non-prostate applications has been limited to date [5, 6]. This is despite the fact that PSMA is highly expressed on the tumor neovasculature of many solid tumors, including RCC [7, 8]. Indeed, a previous case report has demonstrated the ability of a ⁶⁸Ga-labeled small molecule inhibitor of PSMA (⁶⁸Ga-PSMA) to identify sites of disease in a patient with metastatic clear cell RCC [5]. In that report, the authors noted concordance between ¹⁸F-FDG and ⁶⁸Ga-PSMA uptake for all described lesions, though the ⁶⁸Ga-PSMA PET acquisition was notable for improved lesion conspicuity. In combination with the earlier findings utilizing ⁶⁸Ga-PSMA, this report confirms that further study with PSMA radiotracers in metastatic RCC is warranted.