The invention provides diagnostic methods for identifying individuals having a lung cancer (e.g., NSCLC) suitable for treatment a treatment regimen that includes a PD-1 axis binding antagonist (e.g., atezolizumab) after adjuvant therapy (e.g., after a platinum-based adjuvant therapy) and therapeutic methods for treating lung cancer (e.g., NSCLC) in an individual identified as one who may benefit from treatment with a treatment regimen that includes a PD-1 axis binding antagonist (e.g., atezolizumab) to the individual following an adjuvant therapy (e.g., after a platinum-based adjuvant therapy). Also provided are compositions (e.g., a PD-1 axis binding antagonist (e.g., atezolizumab), pharmaceutical compositions thereof, assays thereof, kits thereof, and articles of manufacture thereof) for use in identifying patients suitable for treatment and for treating lung cancer (e.g., NSCLC) in an identified individual.