Grade 3 NENs are aggressive tumours with poor prognosis. PRRT+/- radiosensitising chemotherapy is a potential treatment for disease with high somatostatin receptor (SSTR) expression without spatially discordant FDG-avid disease. We retrospectively evaluated the efficacy of PRRT in G3 NEN.

Kaplan-Meier estimation was used to determine progression-free survival (PFS) and overall survival (OS) defined from start of PRRT. Subgroup analysis was performed for patients with Ki-67 ≤ 55% and >55%. Anatomical response (RECIST 1.1) and toxicity 3 months after PRRT was determined. Disease control rate (DCR) was defined as complete response (CR), partial response (PR) and stable disease (SD) of those with prior progression.

28 patients (M = 17; age 16-78 years; Ki-67 ≤ 55% = 22) were reviewed. 17 patients had pancreatic, 5 small bowel, 3 large bowel, 2 bronchial and 1 unknown primary disease. 25/28 had significant FDG-avid disease prior to treatment. Most had Lu-DOTA-octreotate (median cumulative activity 24.4 GBq, median 4 cycles). Twenty patients had radiosensitising chemotherapy. 89% were treated for disease progression; 79% after prior chemotherapy. Median follow-up was 29 months. The median PFS was 9 months for all patients. 16 patients died (Ki-67 ≤ 55% = 11; Ki-67 > 55% = 5) with median OS of 19 months. For Ki-67 ≤ 55% (N = 22), the median PFS was 12 months and median OS 46 months. For Ki-67 > 55% (N = 6), the median PFS was 4 months and median OS 7 months. On CT imaging, DCR at 3 months post-PRRT was 74%, 35% (8/23) PR and 39% (9/23) SD. Eleven patients received further PRRT due to recrudescent disease after response. Five patients developed progression of discordant FDG-avid disease and were referred for targeted therapy/chemotherapy. Grade 3 and 4 lymphopenia and thrombocytopenia occurred in five and five patients, respectively. No renal or liver toxicity related to treatment was seen.

PRRT achieves clinically relevant disease control with acceptable toxicity in G3 NENs.