Waldenström macroglobulinemia (WM) is a rare lymphoproliferative disorder, defined by the presence of a lymphoplasmacytic cell (LPL) infiltrate in the bone marrow (BM, ≥10% infiltration) and a circulating monoclonal immunoglobulin M (IgM). Here, CD40LG is linked to Waldenstrom macroglobulinemia.