Clinical Efficacy of First and Second Series of Peptide Receptor Radionuclide Therapy in Patients With Neuroendocrine Neoplasm: A Cohort Study

Abstract Background Peptide receptor radionuclide therapy (PRRT) is an established treatment for metastatic neuroendocrine neoplasms (NEN) with positive effects on progression free (PFS) and overall survival (OS), but only limited data exists for the effect of multiple series of PRRT. The aim of this study was to investigate PFS and OS in NEN patients treated with multiple series of PRRT conforming to the ENETS treatment protocol. Methods We included all patients with gastrointestinal (GI), pancreatic and bronchopulmonary (BP) NEN treated with PRRT from 2008 to 2018. We used Kaplan-Meier estimation to evaluate PFS and OS with subgroup analysis of primary tumor, Ki67-index, type of radioisotope and number of PRRT series. Results Of 150 patients, 133 patients were included with female/male 61/72, median age 70 (interquartile range 64–76) years. GI-NEN comprised 62%, pancreatic 23% and BP 11%. Median Ki67-index was 5%. After first PRRT G1- and G2-tumors had PFS of 25 and 22 months, compared to 11 months in G3-NENs (p < 0.05) and PFS was longer in G1/G2 GI-NENs than BP-NEN (30 vs. 12 months, p < 0.05). After retreatment with a second series of PRRT, the overall PFS (G1-G3) was 19 months, with G1- and G2-tumors having the highest PFS of 19 and 22 months, respectively. Overall, the GI and BP tumors had an OS of 54 and 51 months. Conclusions PRRT is an effective therapy with long-term PFS and OS, especially in G1 and G2 NENs, and with better prognosis in GI-NEN compared with BP-NENs. OS and PFS was shorter after the second series of PRRT compared with the first, however results were still encouraging.