The main purpose of this study is to evaluate the efficacy of divarasib compared with investigator's choice of immunotherapy (pembrolizumab or nivolumab) or observation in participants with resected Kirsten rat sarcoma viral oncogene homolog glycine 12 to cysteine (KRAS G12C)-positive Stage II-IIIB NSCLC, regardless of tumor programmed death-ligand 1 (PD-L1) status, who have not achieved pathologic complete response (pCR) following neoadjuvant chemoimmunotherapy.

Inclusion Criteria:

• Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1
• Histological or cytological diagnosis of clinical Stage II-IIIB NSCLC of either non-squamous or squamous histology
• Participants must have had complete resection of NSCLC
• Prior treatment with neoadjuvant immune checkpoint inhibitor (pembrolizumab or nivolumab) in combination with histology-based platinum-based doublet chemotherapy
• Participants must be randomized within 12 weeks of their surgery date
• No evidence of disease recurrence or metastatic disease
• Documentation of the presence of a KRAS G12C mutation

Exclusion Criteria:

• Participants who achieve pCR following neoadjuvant treatment
• Prior treatment with a KRAS inhibitor or any other anti-cancer therapy not otherwise specified in the protocol
• Prior treatment with radiation therapy for NSCLC, with the exception of localized symptom-directed radiation prior to surgical resection
• Resolved Grade 3 or greater immune-related AE or unresolved Grade 2 or greater immune-related AE from neoadjuvant immunotherapy
• Active or history of autoimmune disease or immune deficiency
• Significant cardiovascular disease

For eligible studies, qualified researchers may request access to individual patient level clinical data. See Roche's commitment to transparency of clinical study information here: https://go.roche.com/data\_sharing