Cabozantinib plus Atezolizumab in Advanced, Progressive Endocrine Malignancies: A Multicohort, Basket, Phase II Trial (CABATEN/GETNE-T1914).

[PURPOSE] Multikinase inhibitors have shown efficacy in endocrine neoplasms, and synergism with immune checkpoint inhibitors has been noted in other tumors.

[PATIENTS AND METHODS] This is a prospective, multicenter, open-label, Simon two-stage optimal design, phase II study including patients with advanced and refractory endocrine and neuroendocrine neoplasms in six cohorts: lung well-differentiated neuroendocrine tumors, anaplastic thyroid cancer (ATC), adrenocortical carcinoma (ACC), pheochromocytoma/paraganglioma (PPGL), well-differentiated gastroenteropancreatic neuroendocrine tumors (GEP-NET), and grade 3 extrapulmonary neuroendocrine neoplasms. Patients received atezolizumab 1,200 mg intravenously every 3 weeks plus cabozantinib 40 mg/day orally until disease progression or unacceptable toxicity. The primary objective was the overall response rate (ORR) by RECIST 1.1.

[RESULTS] From October 2020 to December 2022, 93 patients were included. The ORR was 14.3% [95% confidence interval (CI), 1.8-42.8] in ATC (N = 14); 8.3% (95% CI, 1.0-27.0) in ACC (N = 24); 15.4% (95% CI, 1.9-45.5) in PPGL (N = 13), and 16.7% (95% CI, 4.7-37.4) in GEP-NET (N = 24). Lung well-differentiated neuroendocrine tumors and grade 3 extrapulmonary neuroendocrine neoplasms had no responses. The duration of response was 20.4 months in ATC, 13.1 months in ACC, 12.2 months in PPGL, and 15.8 months in GEP-NET. Survival rates at 12 months in ATC and ACC were 47.6% and 47.6%, respectively. No unexpected toxicity was observed.

[CONCLUSIONS] Cabozantinib and atezolizumab were safely administered and showed promising ORR, and preliminary long-term survival rates were observed in aggressive and pretreated ACC and ATC, which warrants further investigation.