HDAC9 and neoplasm: Epigenetic therapy by HDAC inhibition reprograms not only cancer cells, but also the immune system to revitalize “cold” tumors to “hot” tumors by changing the tumor microenvironment and the susceptibility to anti‐tumor immune cells.[43, 44] Unfortunately, due to the prohibitive costs of single‐cell analysis these approaches currently would have limited clinical utility at present (see Supporting Information).