CD274 and neoplasm: Previous studies have shown that PD-L1 expression in unstimulated cells can be suppressed by MAPK inhibitors, and that such inhibitors in combination with PD-1 blockade can efficiently attenuate tumor growth in preclinical models (8, 44), suggesting that MAPK signaling is a key regulator of PD-L1 expression as well as of antitumor immunity.