Dual Somatostatin Receptor/18F-FDG PET/CT Imaging in Patients with Well-Differentiated, Grade 2 and 3 Gastroenteropancreatic Neuroendocrine Tumors

Abstract

Our purpose was to prospectively assess the distribution of NETPET scores in well-differentiated (WD) grade 2 and 3 gastroenteropancreatic (GEP) neuroendocrine tumors (NETs) and to determine the impact of the NETPET score on clinical management. Methods: This single-arm, institutional ethics review board–approved prospective study included 40 patients with histologically proven WD GEP NETs. ⁶⁸Ga-DOTATATE PET and ¹⁸F-FDG PET were performed within 21 d of each other. NETPET scores were evaluated qualitatively by 2 reviewers, with up to 10 marker lesions selected for each patient. The quantitative parameters that were evaluated included marker lesion SUV_max for each tracer; ¹⁸F-FDG/⁶⁸Ga-DOTATATE SUV_max ratios; functional tumor volume (FTV) and metabolic tumor volume (MTV) on ⁶⁸Ga-DOTATATE and ¹⁸F-FDG PET, respectively; and FTV/MTV ratios. The treatment plan before and after ¹⁸F-FDG PET was recorded. Results: There were 22 men and 18 women (mean age, 60.8 y) with grade 2 (n = 24) or grade 3 (n = 16) tumors and a mean Ki-67 index of 16.1%. NETPET scores of P0, P1, P2A, P2B, P3B, P4B, and P5 were documented in 2 (5%), 5 (12.5%), 5 (12.5%) 20 (50%), 2 (5%), 4 (10%), and 2 (5%) patients, respectively. No association was found between the SUV_max of target lesions on ⁶⁸Ga-DOTATATE and the SUV_max of target lesions on ¹⁸F-FDG PET (P = 0.505). ¹⁸F-FDG/⁶⁸Ga-DOTATATE SUV_max ratios were significantly lower for patients with low (P1–P2) primary NETPET scores than for those with high (P3–P5) primary NETPET scores (mean ± SD, 0.20 ± 0.13 and 1.68 ± 1.44, respectively; P < 0.001). MTV on ¹⁸F-FDG PET was significantly lower for low primary NETPET scores than for high ones (mean ± SD, 464 ± 601 cm³ and 66 ± 114 cm³, respectively; P = 0.005). A change in the type of management was observed in 42.5% of patients after ¹⁸F-FDG PET, with the most common being a change from systemic therapy to peptide receptor radionuclide therapy and from debulking surgery to systemic therapy. Conclusion: There was a heterogeneous distribution of NETPET scores in patients with WD grade 2 and 3 GEP NETs, with more than 1 in 5 patients having a high NETPET score and a frequent change in management after ¹⁸F-FDG PET. Quantitative parameters including ¹⁸F-FDG/⁶⁸Ga-DOTATATE SUV_max ratios in target lesions and FTV/MTV ratios can discriminate between patients with high and low NETPET scores.