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 (18)F-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, (111)In-pentetreotide scintigraphy (SRS), and (18)F-FDG PET. Only (18)F-FDG PET-positive lesions with a maximum standardized uptake value (SUVmax) greater than 4.5 or an SUV ratio (SUVmax tumor to SUVmax 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 (18)F-FDG PET finding, with an OS of 119.5 mo (95% confidence interval [CI], 72-∞), than for patients with a positive (18)F-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 (18)F-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 (18)F-FDG PET. At 48-mo follow-up, 100% of patients who had a positive (18)F-FDG PET for disease progression (of which 47% were also SRS-positive) were deceased, and 87% of patients with a negative (18)F-FDG PET were alive (P < 0.0001). The T/NT ratio was the only parameter associated with OS on multivariate analysis.

Conclusion: Overall, (18)F-FDG PET appears to be of major importance in the prognostic evaluation of metastatic GEPNET. A positive (18)F-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 (18)F-FDG PET, which is of greater prognostic utility.

Keywords: FDG; PET; neuroendocrine; prognosis.