CD4 and head and neck squamous cell carcinoma: Key predictive PBMs included baseline CD8<sup>+</sup> T cells, CD3<sup>+</sup> T cells at 12 weeks post-treatment (12w pt), CD4<sup>+</sup> T cells at 6w pt, and CD8<sup>+</sup> T cells at 12w pt.<h4>Conclusion</h4>This study focused on evaluating immunotherapy efficacy and survival differences in R/M HNSCC patients across various clinical background.