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Atezolizumab intravenous (IV) is approved for the treatment of various solid tumours. To improve treatment convenience and health care efficiencies, a coformulation of atezolizumab and recombinant human hyaluronidase PH20 was developed for subcutaneous (SC) use. Part 2 of IMscin001 (NCT03735121) was a randomised phase III, open-label, multicentre, noninferiority study comparing the drug exposure of atezolizumab SC with atezolizumab IV. Eligible patients with locally advanced/metastatic non-small-cell lung cancer were randomised 2 : 1 to receive atezolizumab SC (1875 mg; n = 247) or IV (1200 mg; n = 124) every 3 weeks. The co-primary endpoints were cycle 1 observed trough serum concentration (C trough) and model-predicted area under the curve from days 0 to 21 (AUC 0-21 d). The secondary endpoints were steady-state exposure, efficacy, safety, and immunogenicity. Exposure following atezolizumab SC was then compared with historical atezolizumab IV values across approved indications. The study met both of its co-primary endpoints: cycle 1 observed C trough {SC: 89 μg/ml [coefficient of variation (CV): 43%] versus IV: 85 μg/ml (CV: 33%); geometric mean ratio (GMR), 1.05 [90% confidence interval (CI) 0.88-1.24]} and model-predicted AUC 0-21 d [SC: 2907 μg d/ml (CV: 32%) versus IV: 3328 μg d/ml (CV: 20%); GMR, 0.87 (90% CI 0.83-0.92)]. Progression-free survival [hazard ratio 1.08 (95% CI 0.82-1.41)], objective response rate (SC: 12% versus IV: 10%), and incidence of anti-atezolizumab antibodies (SC: 19.5% versus IV: 13.9%) were similar between arms. No new safety concerns were identified. C trough and AUC 0-21 d for atezolizumab SC were consistent with the other approved atezolizumab IV indications. Compared with IV, atezolizumab SC demonstrated noninferior drug exposure at cycle 1. Efficacy, safety, and immunogenicity were similar between arms and consistent with the known profile for atezolizumab IV. Similar drug exposure and clinical outcomes following SC and IV administration support the use of atezolizumab SC as an alternative to atezolizumab IV. • Atezolizumab SC resulted in noninferior exposure versus atezolizumab IV in patients with NSCLC. • Efficacy, safety, and immunogenicity of atezolizumab SC were similar to atezolizumab IV from IMscin001 and historical data. • Exposure following atezolizumab SC was similar to the exposure seen in other approved clinical studies for atezolizumab IV. • The resulting clinical data support the use of atezolizumab SC as an alternative to atezolizumab IV. [ABSTRACT FROM AUTHOR]