HDAC9 and B-cell chronic lymphocytic leukemia: Notably, belinostat, an inhibitor of histone deacetylase (HDAC), was sanctioned for the treatment of T-cell lymphoma, while ABT-199, a highly selective inhibitor of Bcl-2, was approved for patients with chronic lymphocytic leukemia (CLL) exhibiting a 17p chromosomal deletion [22].