Repeat Peptide Receptor Radionuclide Therapy in Neuroendocrine Tumors: A NET Center of Excellence Experience

IntroductionThe available data for the safety and efficacy of repeat peptide receptor radionuclide therapy (PRRT) are almost exclusively from European centers. We present an updated experience with repeat PRRT in a cohort of US patients with neuroendocrine tumors (NETs) at our NET center of excellence.MethodsWe used our single-center longitudinal NET registry to identify patients who had been previously treated with at least one dose of PRRT (PRRT 1, either 177Lu DOTATATE or 90Y DOTATOC) and following radiographic disease progression were re-treated with a second course of PRRT (PRRT 2). We reviewed patient, tumor and treatment characteristics, objective response rates, and toxicities after PRRT 1 and PRRT 2.ResultsA total of 11 patients were included in the analysis. 45.5% (5/11) of patients received 177Lu DOTATATE PRRT only, both for PRRT1 and PRRT 2, while 54.5% (6/11) of patients received 90Y DOTATOC PRRT for PRRT1. At first restaging scan after PRRT2 (3-6 months), 18.2% (2/11), 36.4% (4/11), and 27.3% (3/11) of patients had PR, SD, and PD, respectively; 2/11 patients (18.2%) died before the first restaging scan. Therefore, 5/11 (45.5%) patients were noted to have disease progression. Median PFS for PRRT1 was 25.4 months and median PFS for PRRT2 was 13.1 months (p = 0.0001). We did not find a statistically significant difference between the occurrence of short and long-term hematological toxicities as well as renal toxicity after PRRT1 and PRRT2.ConclusionWe show that repeat PRRT may benefit select patients and have an acceptable safety profile. In our cohort, PFS was significantly lower after PRRT2 as compared to PRRT1.