IDO1 and breast cancer: To explore the epigenetic mechanisms that regulate PD‐L1 and IDO‐1 expression in ESCC cells, we performed bioinformatics analysis using Chromatin immunoprecipitation (ChIP) sequencing data from the ENCODE database and found that in various malignancies, such as pancreatic cancer, colorectal cancer, cervical cancer, hepatic cell carcinoma, and breast cancer, H3K4me3 marks were enriched in both the PD‐L1 and IDO‐1 promoter regions around the transcription start site (Figure 4A and Figure S4A).