Aims: ⁶⁸Ga-DOTATATE and FDG PET have been increasingly utilised in the investigation of neuroendocrine tumours (NETs) to aid prognostication and guide management. FDG PET avidity is associated with poor prognosis, and FDG positive but ⁶⁸Ga-DOTATATE negative areas may signal the presence of high grade disease. We aimed to investigate the prognostic value of a novel FDG/⁶⁸Ga-DOTATATE grading scheme in patients with metastatic PNETs.

Methods: Consecutive patients from 2011 to 2015 with histologically diagnosed NET who underwent ⁶⁸Ga-DOTATATE and FDG PET scans at RNSH were identified. Patients with metastatic PNET who had both scans within a period of 45 days were eligible for inclusion. A novel scoring scheme was used to grade disease. Paired scans were graded from 1 (⁶⁸Ga-DOTATATE avid, FDG negative disease) to 5 (FDG avid, ⁶⁸Ga-DOTATATE negative disease). The primary endpoint was overall survival from date of first paired scan. The correlation between grading of the first paired scans and overall survival was assessed by calculation of Kaplan-Meier curves and log-rank test.

Results: 26 patients (median age 50 years, 34% female) were eligible for inclusion with median follow-up 8 months for patients still alive. Considered as three groups (Grade 1, Grade 2-4, Grade 5), increased scan grading was associated with poorer overall survival (Grade 1: Not reached, Grade 2-4: Not reached, Grade 5: 11 months; p=0.012, log-rank test for trend).

Conclusions: ⁶⁸Ga-DOTATATE/FDG PET grade correlates with prognosis, with increasing FDG avidity/lack of ⁶⁸Ga-DOTATATE avidity predicting for poorer overall survival. Dual imaging and its prognostic implications for other NETs, as well as potential implications for efficacy of peptide radionuclide receptor therapy, should be investigated further.