Real-world analysis of peptide receptor radionuclide therapy (PRRT) in the treatment of neuroendocrine tumors.

Abstract

e16701 Background: PRRT received FDA approval in 2018 for treatment of somatostatin receptor positive gastroenteropancreatic neuroendocrine tumors (GEPNETs) based on NETTER-1 trial data that included only small bowel grade 1 and 2 neuroendocrine tumors. We present real-world data of PRRT outcomes and implementation from a large tertiary treatment center following approval. Methods: Patients treated with PRRT at University of Iowa between Jan 2018 - July 2019 were included in this retrospective study. Patient and tumor characteristics, cumulative dose and cycles of Lu 177 PRRT administered, treatment course, treatment-related toxicity and responses were reviewed, and 1-year progression-free and overall survival rates were calculated. Results: 67 patients received PRRT, of which 61 completed at least 2 doses. Primary tumor sites included small bowel (64.1%), pancreas (20.3%), and lung (9.4%). 43 (64%) had grade 2 NET; 5 had grade 3 (7.4%). 44 (65.6%) completed 4 cycles of PRRT per FDA approval while 10 received 3 cycles (14.9%). Median duration of follow up was 11.7 months. 53 patients received at least 2 doses and at least one imaging procedure post-PRRT. No complete responses were noted. 9 patients were found to have disease progression at last follow up. 1-year progression-free survival was 78% (95% CI 64-88%). 1-year overall survival was 88% (95% CI 75-94%). Of 23 patients who received fewer than 4 cycles, PRRT was discontinued in 4 (5.9%) due to myelosuppression, specifically thrombocytopenia grade 2 and above. 9 patients discontinued therapy due to change in clinical status or progression per treating physician, 2 experienced carcinoid crisis and 2 had renal function deterioration (preexisting renal disease). 5 patients had previously received PRRT with either Y90 or Lu 177 prior to FDA approval and were retreated in our cohort. 5 patients had preexisting renal disease, including one patient on peritoneal dialysis. Conclusions: We noted a higher rate of treatment discontinuation after 3 cycles, possibly due to heavy pretreatment or treatment of patients with advanced disease, not uncommon after a new therapy is approved and implemented into practice. Discontinuation due to myelosuppression or renal dysfunction was minimal, consistent with NETTER-1 data. Our cohort is unique as it included patients who had received prior PRRT as well as others with preexisting renal dysfunction. Despite this, treatment-related toxicity in our cohort was not significantly higher.