CD274 and head and neck squamous cell carcinoma: In a mouse model of MAPK-activated head and neck squamous cell carcinoma, trametinib, a small molecule MEK inhibitor, inhibited extracellular signal-regulated kinase phosphorylation, promoted MHC-I and PD-L1 expression, and in combination with PD-L1 blockade, overcame resistance to monotherapy, which significantly improved inhibition of tumor growth [106].