An increasing number of studies have shown that HDAC6 is closely related to the occurrence and development of tumors.259,263,264 HDAC6 inhibitors can inhibit cancer cell proliferation, promote apoptosis and have good effects in various malignant tumors, such as multiple myeloma (MM), non-Hodgkin lymphoma (NHL) and other malignant tumors.262,265 However, most HDAC6 inhibitors are poorly selective and act on a variety of HDAC isoforms, especially HDAC1 and HDAC3. Here, HDAC9 is linked to cancer.