Fibroblast activation protein (FAP) has been proposed as a pan-tumor target for PET imaging using FAP-targeted tracers. Here, we explore the potential value of FAP PET in renal tumors. Methods: Six patients with renal tumors (4 with clear cell renal cell carcinoma, 1 with papillary renal cell carcinoma, and 1 with renal oncocytoma) who were included in a prospective imaging study (NCT04147494) underwent [68Ga]Ga-FAPI-46 PET before nephrectomy. FAP PET radiotracer uptake and FAP expression by immunohistochemistry were assessed in the tumors and surrounding renal parenchyma. Results: Tumoral FAP radiotracer uptake was highest in clear cell renal cell carcinoma (median SUVmax, 3.1; range, 2.5-5.3), followed by renal oncocytoma (SUVmax, 1.9) and papillary renal cell carcinoma (SUVmax, 1.1). The FAP PET signal strongly correlated with FAP expression by immunohistochemistry (SUVmax; r = 0.93; P = 0.007). Conclusion: FAP expression in different renal tumors, including renal cell carcinoma, was lower when compared with cancers with known FAP expression, such as sarcoma. Although our data do not favor FAP-based theranostic approaches in renal cell carcinoma, studies in larger cohorts are warranted for conclusive evidence.
Journal of nuclear medicine : official publication, Society of Nuclear Medicine. 2025 Oct 16 [Epub ahead of print]
Adrien Holzgreve, Lena M Unterrainer, Kimberly Flores, Ethan C Lam, Christine E Mona, Johannes Czernin, Brian M Shuch, Anthony E Sisk, Jeremie Calais
Ahmanson Translational Theranostics Division, Department of Molecular and Medical Pharmacology, UCLA, Los Angeles, California., Department of Pathology, UCLA, Los Angeles, California., Jonsson Comprehensive Cancer Center, UCLA, Los Angeles, California; and., Ahmanson Translational Theranostics Division, Department of Molecular and Medical Pharmacology, UCLA, Los Angeles, California; .