Peptide receptor radionuclide therapy (PRRT) for neuroendocrine tumors (NET): A two-year single institution experience

Objectives: Neuroendocrine tumors (NET) are a heterogenous group of tumors, once thought rare, but now show a rising incidence. The tumor often times is indolent, thus leading to a late diagnosis at an advanced metastatic stage. Peptide receptor radionuclide therapy (PRRT) with radiolabeled somatostatin analogue has emerged as a new encouraging systemic treatment modality, especially for unresectable metastasized NETs. PRRT is not only known to reduce tumor burden but also NET-related symptoms, thus increasing quality of life. We present here our initial experience with lutetium-177 (¹⁷⁷Lu) labeled Dotatate since FDA approval in January 2018 in patients with NET and other somatostatin receptor (SSTR) positive tumors.

Methods: Sixty-three patients (33 males and 30 females; 37 - 81-year-old, mean ± SD: 62.1 ± 10.4 years) were treated with PRRT at our institution. Thereof 58 had progressing NETs (32 of the pancreas, 18 of the small intestine, 1 of the coecum, 1 of the appendix, 1 of the stomach and 5 of unknown primary), 3 had a paraganglioma, and 2 had a pheochromocytoma. Treatment was scheduled every 8 weeks for a total of 4 cycles. ⁶⁸Ga-Dotatate PET/CT was performed at baseline, interim after 2 cycles, and following completion of PRRT. RECIST and SSTR density based on change of SUV_max were used to evaluate response to therapy. We assessed progression-free survival (PFS), objective response rate (ORR) and, considering the short follow-up time, an interim overall survival (OS).

Results: 36/63 (57.1%) patients completed all 4 cycles of PRRT, receiving a full dose of 7400MBq each. 10/63 (15.9%) patients had to discontinue treatment (4 after 1^st cycle, 3 after 2^nd cycle, and 3 after 3^rd cycle) due to co-morbidities. 17/63 (27%) patients are still scheduled to receive additional cycles. The 11-month PFS rate was 57% and the 14-month PFS rate was 62%. The ORR was 26%. In the interim OS analysis, 8 deaths occurred from co-morbidities.

Conclusions: In our heterogenous and heavily pretreated patient cohort, the preliminary data show overall good results of PRRT with a high ORR.