ALK and squamous cell carcinoma: U0126 significantly decreased PD-L1 expression at both protein and mRNA levels in the NCI-H1975 lung adenocarcinoma cell line with an EGFR mutation, in the EBC-1 lung squamous cell carcinoma cell line without an EGFR/KRAS/ALK mutation, and in the NCI-H460 lung large cell carcinoma with a KRAS (Q61H) mutation (S3 Fig), suggesting that the MAPK signal contributes to PD-L1 expression irrespective of any histological differences.