CD8A and head and neck squamous cell carcinoma: A preclinical study using mEERL95 cells, which are mouse‐derived HPV‐positive HNSCC models, found that chronic metformin treatment significantly reduced tumor growth velocity (> 50%, p < 0.0001) and increased the CD8+/T‐reg ratio, leading to enhanced tumor immune infiltration. These findings suggest that long‐term metformin administration may potentiate immune checkpoint inhibitors by modulating the tumor immune microenvironment.