Endocrine Abstracts

Introduction: The best timing for PRRT (peptide receptor radionuclide therapy) in the case of pancreatic neuroendocrine tumors (panNETs) is still to define, as randomized prospective trials are lacking. Recent studies suggest that some systemic therapies can affect response to PRRT, favoring an earlier use of the latter.

Objective: To determine the efficacy and toxicity of PRRT, comparing its results when used as a second line systemic therapy (after somatostatin analogs) (Group 1) and as a third or fourth line (after chemotherapy, sunitinib or everolimus) (Group 2).

Methods: A real-world, retrospective study of well-differentiated nonfunctioning panNETS, metastatic and/or unresectable, that completed 3 cycles of PRRT with 177Lu-DOTA-TATE at a tertiary center between 2011 - 2018. The data was collected from clinical records. The statistical analysis was performed in SPSS.

Results: We reviewed a population of 29 patients with a mean age of 55±11 years (52% males). Median time since diagnosis until PRRT was 38 (range: 14-95) months. The majority had grade 2 tumors (64%). Around 89% of patients had hepatic metastasis, 61% lymph node metastasis and 29% other metastases. Median cumulative activity of 19,61 (range: 17-22,2) GBq. A total of 16 patients received PRRT as a 2nd line systemic therapy (Group 1), while 13 patients previously received other systemic therapies (Group 2). Median follow-up time after the first cycle was 31,3 (range: 22-55) months. Median progression-free survival (PFS) was 24,5 (CI 95%: 17 – 32) months and median overall survival (OS) was 46,6 (CI 95%: 20 - 73) months. There was no statistically significant difference of PFS (Group 1: 22,3 (CI 95%: 11-34) Group 2: 24,5 (CI 95%: 15-34); P=0,95) and OS (Group 1: 54,8 (CI 95%: 29 - 81); Group 2: 43,3 (CI 95%: 15-72); P=0,39) between the 2 groups. Around 90% of patients that reported symptoms before treatment, had symptomatic improvement. One patient had clinically significant hepatic toxicity (G3) after the 1st cycle, partially reversible before the 3rd cycle. There were no cases of clinically significant (grade 3/4) hematological or renal toxicity.

Conclusion: PRRT is a safe treatment, associated with symptomatic improvement. PFS was similar between groups, suggesting that PRRT efficacy is not influenced by previous systemic therapies. However, patients receiving PRRT earlier had the longest OS, although not statistically significant. These data can indicate a potential benefit of using PRRT earlier in the treatment sequence. Randomized prospective studies with larger samples are needed to confirm these results.