Background: Data on the efficacy of immune checkpoint inhibitors on delaying or preventing the occurrence of brain metastases (BMs) in metastatic NSCLC without initial BMs is limited. We explored the benefit of first-line atezolizumab versus chemotherapy in the occurrence of BMs in patients without baseline BMs. Methods: Individual patient data from IMpower1301, IMpower131, and IMpower150 were pooled. All patients in the intention to treat population were analyzed. Primary endpoints included BM free survival (BMFS) and the cumulative incidence of BM. Patients without baseline BMs were categorized into two groups: patients who received treatment including atezolizumab (atezolizumab group) and patients who received comparator chemotherapies (chemotherapy group). Results: In 2543 patients without baseline BMs, 87 (3.4%) developed BM, including 58 (3.4%) and 29 (3.4%) in the atezolizumab group and the chemotherapy group, respectively. The median BMFS was 8.31 months (95% CI 7.79-8.67). The cumulative incidence of BM at 6 months, 12 months, and 24 months was 1.9%, 3.1%, and 3.8%, respectively. Compared to the chemotherapy group, BMFS was significantly improved in the atezolizumab group (8.6 months versus 7.3 months, p< 0.001). After taking the competing risk events into account, no significant difference of the cumulative incidence of BM was observed between the two groups (p = 0.671), suggesting that the significantly better BMFS in the atezolizumab group analyzed by Kaplan-Meier method should be due to the lower incidence of extracranial progression or death. Baseline bone metastasis and non-squamous NSCLC were identified as two risk factors for BM. Conclusions: In patients with NSCLC without baseline BMs, first-line atezolizumab improved BMFS but not the cumulative incidence of BM compared to chemotherapy, indicating that atezolizumab could not reduce the intrinsic risk of intracranial tumor spreading.

BM, brain metastasis.