A Phase II Study of Atezolizumab in Combination with Stereotactic Radiation for Patients with Triple-Negative Breast Cancer and Brain Metastasis

Triple-negative breast cancer (TNBC) patients with brain metastases have a poor prognosis and limited treatment options. Preclinical and clinical evidence suggests that radiotherapy may act synergistically with immune checkpoint inhibitors. We conducted an open-label, single-arm, phase II study of atezolizumab plus stereotactic radiosurgery (SRS) in metastatic TNBC patients with brain metastases. The primary endpoint was progression-free survival (PFS) according to the Response Assessment in Neuro-Oncology Brain Metastases (RANO-BM) bi-compartmental model. Secondary endpoints included extracranial objective response rate, overall survival (OS), and safety and tolerability. A safety run-in analysis for dose-limiting toxicity (DLT) was performed after the first 6 patients were enrolled and completed the assessment period. Six patients were enrolled into the safety run-in phase between May 11, 2018 and October 24, 2019. No DLTs were observed, but the study was closed early due to slow accrual. Patients received a median of 2 atezolizumab cycles (range: 2—16), and SRS was administered to all 6 patients. Treatment-related adverse events (TRAEs) occurred in 4 participants (66.7 https://www.clinicaltrials.gov NCT03483012. Trial Open to Accrual: 05/01/2018.