STAT3 and plasma cell myeloma: While IL-6 signals via at least 3 pathways in multiple myeloma, namely STAT3, ERK1/2, and AKT [31, 32], we first biologically validated the impact of YM155 on IL-6/STAT3-signalling, finding a concentration-dependent decrease of phospho-STAT3 in both cell lines after 24 hours under normal growth conditions.