We further explored the expression difference in immune checkpoint genes between the high- and low-3′-UTR piSNV ratio groups in tumor samples (Fig. 2g), and we found that IDO1 and CD274 were inhibitory immune checkpoints with significantly higher expression in high-3′-UTR piSNV ratio groups of ESCC and Liver-HCC (Supplementary Fig. 2e, f). Here, IDO1 is linked to esophageal squamous cell carcinoma.