Fibroblast activation protein inhibitor (FAPI)-negative huge renal cell carcinoma demonstrating an intriguing pattern on [99mTc]Tc-FAPI-46 scintigraphy.

This report describes a 58-year-old man with right flank pain, hematuria, and dysuria, leading to the discovery of a large renal mass via ultrasonography. A contrast-enhanced computed tomography (CT) scan revealed a huge abdominal mass with areas of necrosis and calcification. [99mTc]Tc-FAPI-46 scintigraphy showed photopenic areas and accumulation in a compressed gallbladder, showing an intriguing pattern. A comprehensive surgical resection of the tumor involving the right kidney, adrenal gland, ascending and a portion of transverse colon and liver was successfully performed, and the pathological evaluation confirmed the diagnosis of clear cell renal cell carcinoma (ccRCC). This case represents the pioneering application of [99mTc]Tc-FAPI-46 scintigraphy in ccRCC with sarcomatoid features, demonstrating a lack of avidity.