P974: INTERIM ANALYSIS OF THE LAUNCH STUDY-A MULTICENTER, OPEN-LABEL STUDY OF SELINEXOR, DEXAMETHASONE PLUS CHEMOTHERAPY DRUGS IN RELAPSED/ REFRACTORY MULTIPLE MYELOMA - Chunyan Sun; Baijun Fang; Guangxun Gao; Ai‑li He; Fei Zhao; Junying LI; Chun Zhang; Weiming LI; Hui Cheng; Huili Cai; Bin Chen; Jingming Guo; et al. (HemaSphere, 2023)