A decrease in SM/B of ≥ 8% after three months was associated with a lower median OS of 6.7 vs. 26.2 months, p=0.032.<h4>Conclusions</h4>Automated CT-based body composition analysis, particularly the thoracic SM/B ratio and serum albumin level, provide valuable prognostic information on OS for HNSCC patients receiving immunotherapy and may guide clinical decision-making in this patient population. This evidence concerns the gene ALB and head and neck squamous cell carcinoma.