BR.34 compared the overall survival following an immunotherapy treatment combination of both durvalumab plus tremelimumab with or without chemotherapy in metastatic NSCLC. Participants were allocated by chance to one of two treatment groups. Participants in both groups received durvalumab and tremelimumab every 28 days for 4 cycles followed by durvalumab every 28 days until disease progression. Participants in one group only also received one of two types of chemotherapy during durvalumab and tremelimumab treatment. Patients with squamous cell NSCLC received gemcitabine and cisplatin or carboplatin chemotherapy, and patients with non-squamous NSCLC received pemetrexed and cisplatin or carboplatin chemotherapy.