MYD88 is an adaptor protein in the Toll-like receptor and interleukin 1 receptor pathway which mediates activation of NF-KB. The somatic, activating mutation in MYD88 (p.L265P) has been reported in approximately 90% of lymphoplasmacytic lymphoma (Waldenostrom's macroglobuinemia), 20-30% of cases of diffuse large B cell lymphoma (DLBCL), 10-60% of IgM MGUS, 10% of MALT lymphoma and up to 10% of chronic lymphocytic leukemia. It has not been reported in acute leukemia or multiple myeloma (including IgM myeloma). The L265P mutation increases in NFκB activity, JAK–STAT3 (Janus kinase–signal transducer and activator of transcription 3) signalling and interferon-β production. Targetted therapy using inhibitors of the different components of this pathway are at various stages of investigation. Responses to targeted therapy with Ibrutinib may vary according to MYD88 and CXCR4 mutation status according to some studies.