PDCD1 and neoplasm: EMT is key to tumour cell remodelling for metastasis.5 The interaction between tumour cells and tumour-infiltrating lymphocytes induces the expression of PD-L1 in tumour cells through the STAT pathway; in HNSCC, the expression of PD-L1 is closely related to EMT.25,37,38 These results are consistent with ours, which indicate that, in vivo, PD-1-expressing T cells, B cells, and NK cells interact with OSCC cells, promoting EMT and immune escape.