Outcomes of peptide receptor radionuclide therapy (PRRT) in metastatic grade 3 neuroendocrine tumors (NETs).

e15694 Background:Grade 3 (G3) NETs have a poor prognosis and limited treatment options (usually chemotherapy). PRRT is a potential treatment option if all sites of disease demonstrate high uptake on somatostatin-receptor imaging (SSRI). We retrospectively evaluated the efficacy of PRRT in G3 NETs. Methods: We reviewed records of patients with metastatic G3 NETs (Ki-67 > 20%) who received PRRT at our institution. Patients were treated with up to 5 cycles of PRRT, predominantly 177Lu-DOTA-octreotate. Further maintenance PRRT was administered upon progression if deemed suitable on SSRI. Radio-sensitizing chemotherapy was administered unless contra-indicated. Kaplan-Meier estimate was used to determine median overall survival (OS) and median time to new treatment/death (TNTD) defined from start of PRRT. Subgroup-analysis was performed for patients with Ki67 < 55% and ≥55%. Results: 26 patients with metastatic G3 NET received PRRT; 22 combined with chemotherapy (capecitabine/temozolomide (n = 12), 5-fluorouracil or capecitabine (n = 8), other (n = 2)). 58% were male. The median age was 62 (range 16-78 years). 61% had pancreatic NET, 19% small bowel, 8% lung, 8% unknown primary, 4% rectal. 77% had received at least one line of prior chemotherapy. 54% received prior platinum-based chemotherapy. Median follow-up was 33 months (range 8-83 months). Patients received a median of 4 cycles of PRRT (range 1-15). The estimated median OS from start of PRRT was 18 months: for Ki-67 < 55% (n = 21), 20 months; and Ki-67≥ 55% (n = 5), 9 months. The estimated median TNTD was 12 months: for Ki-67 < 55%, 16 months; and Ki-67≥55%, 4 months. 31% of patients were alive without a change in treatment modality following PRRT. Conclusions: In thispoor prognosis G3 NET cohort of whom 77% had received prior chemotherapy, a median OS of 18 months from start of PRRT is encouraging and warrants further study. PRRT is a promising treatment option for patients with G3 NET with high somatostatin-receptor expression selected by SSRI.