PDCD1 and head and neck squamous cell carcinoma: Meta-analysis showed that HNSCC patients expressing PD-L1 may have a better tumor response and PFS when receiving PD-1 or PD-L1 inhibitor monotherapy, PD-L1 positive patients with ≥ 1% expression had a weighted mPFS of 3.34 months (range 1.9–13.4) [48].