Efficacy of repetitive somatostatin receptor-targeted radionuclide therapy with 90Y- and/or 177Lu-DOTATOC in patients with neuroendocrine tumors

1520 Purpose: We investigated the efficacy of the first (R-PRRT) and second (RR-PRRT), retreatment of 90Y- and/or 177Lu-DOTATOC somatostatin receptor-targeted radionuclide therapy (PRRT) in patients with grade 1/2 bronchial neuroendocrine tumor (NET) or gastroenteropancreatic NET (GEP-NET). Materials and Methods: All patients with grade 1/2 recurrent or progressive inoperable bronchial NET or GEP-NET treated at our institution were eligible for this retrospective study. The time interval between treatments as a measure of time to progression served as primary study endpoint. At each retreatment one 90Y- and/or 1-2 177Lu-DOTATOC treatment cycles were performed. Results: Between March 2000 and July 2018, 523 patients (323 male and 200 female; age 59 ± 11 yrs) underwent a first retreatment for recurrent or progressive disease. Out of the 523 patients, 150 patients (29%) underwent a second, and 42 patients (8%) a third retreatment. The median time interval was 27.2 months (95% confidence interval (CI), 25.8-28.5 months) between the initial treatment and the first retreatment, 19.7 months (CI, 17.6-21.9 months) between the first and the second retreatment (p<0.01), and 18 months (CI 16.9-20.7 months) between the second and the third retreatment (p=0.59). Conclusions: 90Y- and/or 177Lu-DOTATOC retreatments are highly efficient in patients with grade 1/2 NET. However, the initial treatment showed somewhat higher efficacy compared to the first and second retreatment.