Waldenstrom macroglobulinemia (WM) is a rare chronic cancer which can be classified as a low grade (indolent) type of lymphoma. It is caused by the neoplastic proliferation of the lymphocyte-plasma cell system that produces excessive amounts of monoclonal IgM molecules containing one class of light chains. The abnormal plasma cells multiply out of control and they invade the bone marrow, lymph nodes, and spleen. The excess IgM produced by abnormal plasma cells causes hyperviscosity of the blood.