High Prognostic Value of ¹⁸F-FDG PET for Metastatic Gastroenteropancreatic Neuroendocrine Tumors: A Long-Term Evaluation

Abstract

This study aimed to evaluate the long-term prognostic usefulness of ¹⁸F-FDG PET for patients with metastatic gastroenteropancreatic neuroendocrine tumors (GEPNETs). Methods: Thirty-eight patients with metastatic GEPNETs were prospectively enrolled. Initial check-up comprised CT scan, ¹¹¹In-pentetreotide scintigraphy (SRS), and ¹⁸F-FDG PET. Only ¹⁸F-FDG PET–positive lesions with a maximum standardized uptake value (SUV_max) greater than 4.5 or an SUV ratio (SUV_max tumor to SUV_max nontumoral liver tissue, or T/NT ratio) of 2.5 or greater were considered positive for prognosis—that is, indicating a poor prognosis. Progression-free survival (PFS) and overall survival (OS) were estimated using the Kaplan–Meier method. Factors associated with survival were assessed with univariate and multivariate analyses, using the Cox regression model. Results: Median PFS and OS were significantly higher for patients with a negative ¹⁸F-FDG PET finding, with an OS of 119.5 mo (95% confidence interval [CI], 72–∞), than for patients with a positive ¹⁸F-FDG PET finding (only 15 mo [95% CI, 4–27]) (P < 10⁻³). Median PFS and OS were significantly higher for the patient group that had a positive SRS than the group with a negative SRS (P = 0.0002). For patients with a positive SRS, PFS and OS were significantly shorter when the ¹⁸F-FDG PET finding was positive: 19.5 mo (95% CI, 4–37) for PFS and 119.5 mo (95% CI, 81–∞) for OS (P < 10⁻³). In the patient group with a low-grade GEPNET and a positive SRS, PFS and OS were also significantly lower for patients with a positive ¹⁸F-FDG PET. At 48-mo follow-up, 100% of patients who had a positive ¹⁸F-FDG PET for disease progression (of which 47% were also SRS-positive) were deceased, and 87% of patients with a negative ¹⁸F-FDG PET were alive (P < 0.0001). The T/NT ratio was the only parameter associated with OS on multivariate analysis. Conclusion: Overall, ¹⁸F-FDG PET appears to be of major importance in the prognostic evaluation of metastatic GEPNET. A positive ¹⁸F-FDG PET with an SUV ratio (T/NT) of 2.5 or greater was a poor prognostic factor, with a 4-y survival rate of 0%. A positive SRS does not eliminate the need for performing ¹⁸F-FDG PET, which is of greater prognostic utility.