Obviously, high expression of the four genes (DDX56, CTSL, ZC3H12D, and PSMC5) could promote the expression of PD-L1 as they have been proven to be promising biomarkers and immunotherapy targets in a variety of tumors, including colorectal cancer (Kouyama et al., 2019; He et al., 2021), NSCLC (Wu et al., 2021; Chen et al., 2022), and gastric cancer (Pan et al., 2020b). Here, CTSL is linked to gastric cancer.