False-positive [68Ga]Ga-FAPI-04 PET/CT Following Treatment of 177Lu-DOTATATE PRRT in a Patient With Metastatic High-grade Well-differentiated Neuroendocrine Tumor

We present a high-grade well-differentiated NET with large lesions that demonstrated both SSTR and [18F]F-FDG avidity on baseline PET/CT, an outstanding response following 177Lu-DOTATATE-PRRT with complete resolution of SSTR and [18F]F-FDG uptake, and significant size reduction of liver lesions. Non-SSTR and non-[18F]F-FDG-avid change was noted in segment V, demonstrated uptake on [68Ga]Ga-FAPI-04 PET/CT, and confirmed as fibrotic changes post-PRRT. Following PRRT, analysis of [68Ga]Ga-FAPI-04 PET/CT in well-differentiated NET is important to avoid misinterpretation. Benign fibrosis following treatment may show FAPI uptake as a possible source of false-positive findings on [68Ga]Ga-FAPI-04 PET/CT in the evaluation of NET.