High Tumor Uptake on ¹⁸F-FDOPA PET/CT Indicates Poor Prognosis in Patients with Metastatic Midgut Neuroendocrine Tumors: A Study from the Groupe d'étude des Tumeurs Endocrines and ENDOCAN-RENATEN Network

PET/CT with 6-¹⁸F-fluoro-l-dopa (¹⁸F-FDOPA) has high diagnostic performance for midgut neuroendocrine tumors (NETs). We explored the prognostic role of ¹⁸F-FDOPA PET/CT uptake in metastatic midgut NETs. Methods: We included, in a test cohort (n = 166) and a full external validation cohort (n = 86), all consecutive patients with metastatic midgut NETs who underwent ¹⁸F-FDOPA PET/CT in 5 expert centers from 2010 to 2021. We measured the maximal uptake (SUV_max and SUV_peak) of the tumor and nontumor liver on each ¹⁸F-FDOPA PET/CT scan. We measured overall survival (OS) from the time of PET/CT and assessed prognostic factors using Kaplan-Meier and multivariable Cox proportional-hazards analyses in the test cohort, with replication in the validation cohort. Results: Patients had similar characteristics in both cohorts. In the test cohort, median follow-up was 60.3 mo. Patients with an SUV_peak tumor-to-liver (T/L) ratio of more than 4.2 had significantly shorter survival than those with a ratio of 4.2 or less (P = 0.01), with a 5-y OS rate of 74.1% ± 4.5% versus 95% ± 3.4%, respectively. On multivariable analysis, an SUV_peak T/L ratio of more than 4.2 remained associated with shorter OS (hazard ratio, 2.30; 95% CI, 1.02-5.22; P = 0.046) after adjustment for age, grade, number of previous lines, number of metastatic sites, and presence of carcinoid syndrome. In the validation cohort, the 5-y OS rate was 100% versus 57.8% ± 12.5% in patients with an SUV_peak T/L ratio ≤ 4.2 or > 4.2, respectively (P = 0.075). An increasing SUV_peak T/L ratio over time tended to have a pejorative prognostic impact. Conclusion: Tumor uptake on ¹⁸F-FDOPA PET/CT is an independent prognostic factor in patients with metastatic midgut NETs.