Background : Evidence suggests that sarcopenia is a significant predictive factor of worst outcomes and treatment-associated toxicities in patients with metastatic solid tumours. The aim of this study was to explore the relationship between low muscle mass and clinical outcomes and immune-related severe toxicities (IrST) in patients treated with immune checkpoint inhibitors (ICIs). Methods : A retrospective cohort of 261 consecutive metastatic solid tumour patients treated with ICIs were included in our study. Low muscle mass was defined as skeletal muscle index <41 cm2/m2 for females and <43 cm2/m2 for males if body mass index (BMI) <25 kg/m2 or <53 cm2/m2 if BMI ≥ 25 kg/m2. Severe toxicities (ST), including grade III-IV toxicities and side effects leading to treatment interruption, were recorded. Results : The majority of patients (n = 179; 69%) included in this study had metastatic lung cancer. The prevalence of low muscle mass was 47%. The median progression-free survival (PFS) was 32.2 weeks for low muscle mass patients and 24.3 weeks for non-low muscle mass patients (adjusted HR, 0.80; 95% CI, 0.60–1.055; p = 0.11). For low muscle mass and non-low muscle mass lung cancer patients, median PFS was 24.0 weeks and 18.8 weeks (adjusted HR, 0.70; 95% CI, 0.50–0.98; p = 0.04) and median overall survival was 50.7 weeks and 41.1 weeks (adjusted HR, 0.77; 95% CI, 0.54–1.10, p = 0.15) respectively. Immune-related severe toxicities occurred in 3.3% and 9.4% of low muscle mass and non-low muscle mass patients respectively (adjusted OR, 0.69; 95% CI: 0.31–1.49; p = 0.35). Conclusion : No difference in outcomes and safety was observed for low muscle mass and non-low muscle mass patients treated with ICIs.< Réduire