•Small cell lung cancer (SCLC) is a highly aggressive type of lung cancer.•Atezolizumab plus chemotherapy improves overall survival in 1st-line treatment of extensive SCLC.•IFCT-1905 CLINATEZO studied consecutive patients receiving this regimen in France.•Our studyreproduced in a real life setting thekey survival outcomesof the landmark trial. Small cell lung cancer (SCLC) has a tendency towards recurrence and limited survival. Standard-of-care in 1st-line is platinum-etoposide chemotherapy plus atezolizumab or durvalumab,based on landmarkclinical trials. IFCT-1905 CLINATEZO is a nationwide, non-interventional, retrospectivestudy of patients with extensive-SCLC receivingatezolizumab plus chemotherapy as part of French Early Access Program. Objectives were to analyse effectiveness,safetyand subsequent treatments. The population analyzed included 518 patients who received atezolizumabin 65 participating centers. There were 66.2% male,mean age was 65.7 years; 89.1% had a performance status (PS) 0/1 and 26.6% brain metastases. Almost all(95.9%) were smokers. Fifty-five (10.6%) received at least 1 previous treatment. Median number of atezolizumab injections was 7.0 (range 1.0–48.0) for a median duration of 4.9 months (95% CI 4.5–5.1). Atezolizumab was continued beyond progression in 122 patients (23.6%) for a median duration of 1.9 months (95% CI: 1.4–2.3). Best objective response was complete and partialin 19 (3.9%) and 378 (77.1%)patients. Stable diseasewas observed in 50 patients (10.2%). Median follow-up was30.8 months (95% CI: 29.9–31.5). Median overall survival (OS), 12-, 24-month OS rates were 11.3 months (95% CI: 10.1–12.4), 46.7% (95% CI 42.3–50.9) and 21.2% (95% CI 17.7–24.8). Median real-world progression-free survival, 6-, 12-month rates were 5.2 months (95% CI 5.0–5.4), 37.5% (95% CI 33.3–41.7) and 15.2% (95% CI 12.2–18.6). For patients with PS 0/1, median OS was 12.2 months (95% CI 11.0–13.5). For patients with previous treatment, median OS was 14.9 months (95% CI 10.1–21.5). Three-hundred-and-twenty-six patients(66.4%) received subsequent treatment and27 (5.2%) were still underatezolizumabat date of last news. IFCT-1905 CLINATEZO shows reproductibility, in real-life,ofIMpower-133survival outcomes, possibly attributed to selection of patients fit for this regimen, adoption of pragmatic approaches,including concurrent radiotherapy and treatment beyond progression.