CD274 and neoplasm: Inhibiting DNA methylation by specifically targeting DNA methyltransferase; low concentration of 5‐AZA significantly inhibits HCC cell proliferation, invasion, migration and other malignant biological activities; when used in combination with monoclonal antibodies of PD‐L1, 5‐AZA increases the ratio of cytotoxic T lymphocytes in the tumour microenvironment and prevents tumour progression by increasing lymphocytes’ tumour‐killing capacity