Is There a Role of FAPI Pet in Renal and Bladder Cancer?

Fibroblast activation proteins (FAPs) are highly expressed in cancer-associated fibroblasts within the tumor microenvironment. Radiolabeled FAP inhibitors (FAPIs) either with 68Ga and 18F can assess the tumor stroma, thus offering a complementary perspective to other imaging modalities. Herein, we aimed to summarize current evidence on FAPI-based imaging in renal cell carcinoma (RCC) and bladder cancer (BC). Moreover, we addressed some perspectives about the utility of FAPI as a theragnostic agents in these urogenital cancers. Across the studies, emerged that FAP expression correlates with tumor aggressiveness, immune evasion, and poor prognosis in both RCC and BC. Indeed, clinical experiences demonstrate that FAPI PET achieves higher tumor-to-background ratios and improved detection of metastatic lesions, mainly peritoneal carcinomatosis and hepatic metastases, as compared with [¹⁸F]FDG. However, urinary excretion limits primary tumor assessment of FAPI like FDG imaging. Early trials of FAPI-based radioligand therapies, including [¹⁷⁷Lu]FAPI-2286, show promising safety and preliminary efficacy. Based on the current premises, FAPI seems a promising agent for genitourinary oncology, requiring further assessment through prospective studies.