Representative 4 μm slices were prepared from FFPE tissue blocks. In short, all tissue slices were exposed to 3% hydrogen peroxide (OriGene; PV-6001) for 10 mins to inhibit the activity of endogenous peroxidase, and heat-mediated antigen retrieval was performed through Tris/EDTA buffer with 8 pH (OriGene; ZLI-9066). Afterwards, 200 μL PD-L1 antibody (Abcam, clone 28–8, monoclonal, 1:400, anti-rabbit) and tissue slices were incubated in a wet box at 4°C overnight, and then HRP-coupled goat anti-rabbit IgG secondary body (OriGene, PV-6001) was added. After addition, they were placed at 37°C for 30 mins, and incubated with 3, 3-diamino benzidine (DAB) (OriGene; ZLI-9017) at indoor temperature for 5 m. In the end, the slices were dried out and immobilized. Negative (no primary antibody) and positive (amniotic membrane roll) controls were adopted in each running. The staining results were interpreted by professional pathologists according to antibody specification. The specific positive PD-L1 was located in cell membrane and cytoplasm. Tumor cells with positive expression rate of PD-L1 ≥1％ were considered as positive tumor cells, and recorded as TC1, and those with the rate <1％ were considered as negative tumor cells, and recorded as TC0.20 (link)