Guerriero et al22 found that Class IIa HDAC inhibitor TMP195 can promote macrophages towards an anti‐tumor phenotype with enhanced capacity to activate cytotoxic T lymphocytes by regulating its gene expression in mouse model of breast cancer, combining TMP195 with PD‐1 inhibitor can significantly enhance the durability of tumor reduction. Here, HDAC9 is linked to breast cancer.