The L265P mutation in MYD88 is very frequent in tumor cells of Waldenström’s macroglobulinemia (WM), and activates NF-kappaB through IRAK1 and IRAK4. We examined the effect of the IRAK1/4 inhibitor R191 on two cell lines of WM. Gene expression profiling suggested that R191 reduced activity of AKT and mTOR signaling, consistent with other assays and functional studies. Other changes suggested reduced proliferation and MYC activity, and an ER stress response. Overall design: Cell lines BCWM.1 and MWCL-1 were treated with R191 at 1.25 uM for 24 hr, and compared to untreated cells.