Waldenström's macroglobulinemia (WM, also known as lymphoplasmacytic lymphoma) is cancer affecting B cells, a type of white blood cell. The main attributing antibody is immunoglobulin M (IgM). WM is an "indolent lymphoma," (i.e., one that tends to grow and spread slowly). It is a type of lymphoproliferative disease, which shares clinical characteristics with the indolent non-Hodgkin lymphomas.