Phase II testing suggests that atezolizumab, a humanized anti-programmed death-ligand 1 (PD-L1) monoclonal antibody, is an effective treatment for advanced non-small cell lung cancer (NSCLC) in patients with confirmed PD-L1 expression. The BIRCH study compared the drug's effect across samples of patients with different PD-L1 levels. The study population included 659 advanced NSCLC patients, 46% of whom had the highest levels of PD-L1 expression: TC3 or IC3. Participants were assigned to one of three cohorts based on whether they were receiving atezolizumab as initial treatment, second-line therapy, or third-line or higher, with the TC3 and IC3 patients distributed evenly across the groups. I.V. atezolizumab was administered every 3 weeks to all patients, and objective response rates were assessed after a minimum followup of 1 year. Overall response rates were 22%, 19%, and 18%, respectively, for patients undergoing first-, second-, and third-line or higher treatment. By comparison, the corresponding response rates for TC3 and IC3 patients in those cohorts were 31%, 26%, and 27%. Overall survival was a median 23.5 months for the first-line group as a whole but 26.9 months for first-line patients with high PD-L1 expression, with a similar pattern emerging across the other cohorts. "BIRCH demonstrated responses with atezolizumab monotherapy with PD-L1 selected advanced NSCLC, with good tolerability," the researchers report in the Journal of Clinical Oncology. "PD-L1 status may serve as a predictive biomarker for identifying patients most likely to benefit from atezolizumab."