Predictors of outcome in patients with neuroendocrine neoplasm (NEN) undergoing FDG PET prior to PRRT

Background: 18-Fluorodeoxyglucose (FDG) PET avidity in NENs has been associated with higher grade disease. Avidity and high SUVmax have been demonstrated to predict poor outcome. Quantitative metrics of FDG PET, specifically metabolic tumour volume (MTV) and total lesion glycolysis (TLG), have been shown to be prognosticators in other malignancies, but these have not been investigated to date in NETs.

Methods: Patients with NEN undergoing PRRT at Royal North Shore Hospital who underwent FDG PET prior to therapy were retrospectively included (2012-17). Images were analysed using MIM software version 6.8.3, with automated segmentation (SUV cutoff of 4) followed by contour verification by a nuclear medicine physician and manual segmentation where required. Variables collected included patient age, WHO 2010 histological grade, MTV, TLG, and SUVmax/peak. The median MTV and TLG were used to dichotomize the cohort. The primary outcome was progression-free survival (PFS), and the secondary outcome was overall survival (OS). Survival curves were compared using the log-rank test.

Results: 49 patients were included (median age 60, 43% female). Primary site: 49% small bowel, 29% pancreas, 22% other. Grade for GEPNENs: G1 31%, G2 55%, G3 7%, unknown 7%. Median MTV was 3.15mL and TLG was 15.5. Patients with high MTV had worse median PFS compared to those with low MTV (19.7mo vs 26.6mo, HR 2.56, 95% CI 1.14-5.73, p=0.02), with the same findings for TLG (19.7mo vs 26.6mo, HR 2.56, p=0.02). Patients with higher grade disease were more likely to have high MTV (p=0.04) and TLG (p=0.04). PFS was shorter in patients with extrahepatic disease compared to those without (19.7mo vs 22.5mo, HR 2.3, 95% CI 1.004-5.4, p=0.049), but was not significantly affected by histological grade or SUVmax/peak. Overall survival was not significantly different between patients with high and low MTV (p=0.23).

Conclusions: Quantitative analysis of FDG PET in NEN is feasible. High MTV/TLG are predictors of poor prognosis in NEN. Further analyses are underway to investigate a larger cohort of NEN patients.