Assessment of Clinical Response Following Atezolizumab and Bevacizumab Treatment in Patients With Neuroendocrine Tumors: A Nonrandomized Clinical Trial.

Importance:Therapies for patients with advanced well-differentiated neuroendocrine tumors (NETs) have expanded but remain inadequate, with patients dying of disease despite recent advances in NET therapy. While patients with other cancers have seen long-term disease control and tumor regression with the application of immunotherapies, initial prospective studies of single-agent programmed cell death 1 inhibitors in NET have been disappointing. Objective:To evaluate the response rate following treatment with the combination of the vascular endothelial growth factor inhibitor bevacizumab with the programmed cell death 1 ligand 1 inhibitor atezolizumab in patients with advanced NETs. Design, Setting, and Participants:This single-arm, open-label nonrandomized clinical study in patients with rare cancers included 40 patients with advanced, progressive grade 1 to 2 NETs (20 with pancreatic NETs [pNETs] and 20 with extrapancreatic NETs [epNETs]) treated at a tertiary care referral cancer center between March 31, 2017, and February 19, 2019. Data were analyzed from June to September 2021. Interventions:Patients received intravenous bevacizumab and atezolizumab at standard doses every 3 weeks until progression, death, or withdrawal. Main Outcomes and Measures:The primary end point was objective radiographic response using Response Evaluation Criteria in Solid Tumors, version 1.1, with progression-free survival (PFS) as a key secondary end point. Results:Following treatment of the 40 study patients with bevacizumab and atezolizumab, objective response was observed in 4 patients with pNETs (20%; 95% CI, 5.7%-43.7%) and 3 patients with epNETs (15%; 95% CI, 3.2%-37.9%). The PFS was 14.9 (95% CI, 4.4-32.0) months and 14.2 (95% CI, 10.2-19.6) months in these cohorts, respectively. Conclusions and Relevance:In this nonrandomized clinical trial, findings suggest that clinical responses in patients with NET may follow treatment with the combination of bevacizumab and atezolizumab, with a PFS consistent with effective therapies. Trial Registration:ClinicalTrials.gov Identifier: NCT03074513.