HDAC9 and hematopoietic and lymphoid cell neoplasm: Having been granted fast-track designation by the FDA for treatment of relapsed or refractory DLBCL after positive results from phase II studies (CURIS, 2019), the first PI3K/HDAC dual inhibitor GUDC-907 was investigated in clinical trials, which inspired us to observe the antitumor activity of compound 23 against hematologic tumors.