LAUSR

Purpose Rarely, well-differentiated gastro-entero-pancreatic neuroendocrine tumors (GEP NETs) can have positive uptake on 18F-fluorodeoxyglucose-PET/computerized tomography (18F-FDG-PET/CT), with or without a positive 68Ga-PET/CT. We aim to evaluate the diagnostic role of 18F-FDG-PET/CT in patients with well-differentiated GEP NETs. Methods We retrospectively reviewed a chart of patients diagnosed with GEP NETs between 2014 and 2021, at the American University of Beirut Medical Center, who have low (G1; Ki-67 ≤2) or intermediate (G2; and Ki-67 >2–≤20) well-differentiated tumors with positive findings on FDG-PET/CT. The primary endpoint is progression-free survival (PFS) compared to historical control, and the secondary outcome is to describe their clinical outcome. Results In total 8 out of 36 patients with G1 or G2 GEP NET met the inclusion criteria for this study. The median age was 60 years (range 51–75 years) and 75% were male. One patient (12.5%) had a G1 tumor whereas 7 (87.5%) had G2, and seven patients were stage IV. The primary tumor was intestinal in 62.5% of the patients and pancreatic in 37.5%. Seven patients had both 18F-FDG-PET/CT and 68Ga-PET/CT positive and one patient had a positive 18F-FDG-PET/CT and negative 68Ga-PET/CT. Median and mean PFS in patients positive for both 68Ga-PET/CT and 18F-FDG-PET/CT were 49.71 months and 37.5 months (95% CI, 20.7–54.3), respectively. PFS in these patients is lower than that reported in the literature for G1/G2 NETs with positive 68Ga-PET/CT and negative FDG-PET/CT (37.5 vs. 71 months; P = 0.0217). Conclusion A new prognostic score that includes 18F-FDG-PET/CT in G1/G2 GEP NETs could identify more aggressive tumors.