The study conducted by Jeon et al. 29 measured the frequency of classical monocytes (cMonocyte) and PD-L1-expressing classical monocytes (cMonocyte-PDL1) in blood of 45 HCC patients treated with PD-1 ICI (nivolumab) and calculated the on-treatment monocyte index by dividing cMonocyteD7/D0 by cMonocyte-PDL1D7/D0, in which cMonocyteD7/D0 and cMonocyte-PDL1D7/D0 were defined as the fold change in the frequency of cMonocyte and cMonocyte-PDL1 at day 7 over day 0 after treatment initiation, respectively. Here, CD274 is linked to hepatocellular carcinoma.