In an in vitro study performed by Shayan et al., it was found that Tim-3 was upregulated in head and neck squamous cell carcinoma (HNSCC) tumor infiltrating lymphocytes (TILs) after PD-1 blockade, suggesting a potential mechanism of escape from or resistance to PD-1 blockade [122]. This evidence concerns the gene PDCD1 and head and neck squamous cell carcinoma.