Atezolizumab (Tecentriq®), a fully humanized, monoclonal anti-programmed cell death ligand-1 (PD-L1) antibody, is the first immune checkpoint inhibitor to be approved, in combination with carboplatin and etoposide, for the treatment of adult patients with extensive-stage small cell lung cancer (ES-SCLC). Approval was based on primary data from the multinational phase I/III IMpower133 trial in PD-L1-unselected patients with previously untreated ES-SCLC. In this trial, induction therapy with atezolizumab plus carboplatin and etoposide followed by maintenance therapy with atezolizumab alone significantly prolonged overall survival (OS) and progression-free survival (PFS) compared with carboplatin and etoposide alone. The addition of atezolizumab to chemotherapy was generally well tolerated, with no new safety signals being identified beyond those previously reported for the individual agents. The most common grade 3-4 treatment-related adverse events with this regimen were haematological; the most common immune-related adverse events included rash and hypothyroidism. Importantly, the addition of atezolizumab to chemotherapy improved survival outcomes without adversely impacting patient-reported health-related quality of life (HRQOL). Thus, atezolizumab in combination with carboplatin plus etoposide has emerged as a valuable option for the first-line treatment of ES-SCLC and is being accepted as a standard of care in this setting.