RT Journal Article SR Electronic T1 Differentiating Between Mixed Neuroendocrine Non-Neuroendocrine Neoplasms (MiNEN) and Other Subtypes of NEN using Fibroblast Activation Protein Inhibitor (FAPI)-Directed PET JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 2990 OP 2990 VO 63 IS supplement 2 A1 Weich, Alexander A1 Wild, Vanessa A1 Higuchi, Takahiro A1 Meining, Alexander A1 Rowe, Steven A1 Pomper, Martin A1 Mielert, Kilian A1 Rosenwald, Andreas A1 Buck, Andreas A1 Serfling, Sebastian A1 Werner, Rudolf YR 2022 UL http://jnm.snmjournals.org/content/63/supplement_2/2990.abstract AB 2990 Introduction: Fibroblast activation protein (FAP) is overexpressed in highly aggressive gastroenteropancreatic neuroendocrine neoplasms (NEN). We aimed to elucidate the diagnostic performance of non-invasive FAP inhibitor-directed PET using [68Ga]FAPI when compared to the reference radiotracer [18F]FDG in patients with subtypes of poorly differentiated NEN.Methods: 16 patients with metastasized, high grade NEN [neuroendocrine tumor (NET) G2/G3, n=7; neuroendocrine carcinoma (NEC), n=4, and mixed neuroendocrine non-neuroendocrine neoplasms (MiNEN), n=5] underwent [68Ga]FAPI and [18F]FDG PET/CT without treatment between scans. We compared FAPI-based tumor volume (TV) in patients affected with MiNEN to all other subtypes of NEN and identified patients eligible for a FAP-directed endoradiotherapy (ERT).Results: [68Ga]FAPI visualized tumor lesions in 16/16 subjects (100%), which was comparable to [18F]FDG (15/16, 93.8%). On a lesion-basis, none of the radiotracers detected significantly more lesions ([18F]FDG, 9.5±5.3 vs. [68Ga]FAPI, 7.3±3.5, P=0.2). MiNEN patients demonstrated significantly higher FAPI-TV (119.9±57.4) when compared to all other subtypes of NEN (33.4±31.6, P=0.001). Based on a visual assessment including intensity of uptake and widespread disease, MiNEN patients (5/5, 100%) were considered eligible for FAPI-directed ERT (all other types, 4/11 (36.4%)).Conclusions: In aggressive NEN, diagnostic accuracy of [68Ga]FAPI-PET/CT is not inferior when compared to [18F]FDG and may allow to differentiate between patients with MiNEN and other poorly differentiated NEN subtypes. In addition, FAPI-directed ERT may be feasible in patients with MiNEN.