PDCD1 and head and neck squamous cell carcinoma: The combination of anti-PD-1 immunotherapy and BMI1 inhibition significantly increased CD8+ T-lymphocyte infiltration in the TME, thereby inhibiting HNSCC invasive growth and metastasis.145 These novel findings provide a foundation in developing combination therapies targeting CSCs and improving the immune response, which holds promise for treating diverse malignancies.