The current advances and future directions of PD-1/PD-L1 blockade in head and neck squamous cell carcinoma (HNSCC) in the era of immunotherapy

•The mechanism of upregulation of PD-L1 expression was associated with HPV status.•The PD-L1 expression of HNSCC relates to the progression and prognosis of tumor.•PD-1/PD-L1 inhibitors shows prospects in the treatment of R/M HNSCC and LA HNSCC.•Exploration of new combination therapy strategy and treatment methods in HNSCC is ongoing.