S100A9 and hepatocellular carcinoma: Furthermore, our in vivo studies revealed that inhibiting S100A9 can synergistically enhance the efficacy of anti-PD-1 drugs in the eradication of hepatocellular carcinoma.<h4>Conclusions</h4>Our study underscores the significance of S100A9<sup>+</sup>CD14<sup>+</sup> monocytes in predicting inadequate response to ICB treatment and provides insights into the monocyte cell-intrinsic mechanisms of resistance to ICB therapy.