This is a rare, chronic cancer that affects white blood cells called B lymphocytes, or B cells. These cells form in the lymph nodes and the bone marrow, the soft, spongy tissue inside bones, and are an important part of the body's immune (defense) system. Some B cells become plasma cells, which make, store, and release antibodies. Antibodies help the body fight viruses, bacteria, and other foreign substances. In Waldenstrom's macroglobulinemia, abnormal B cells multiply out of control. They invade the bone marrow, lymph nodes, and spleen and produce excessive amounts of an antibody called IgM.

An indolent (slowly progressing) type of non-Hodgkin's lymphoma marked by abnormal levels of IgM antibodies in the blood and an enlarged liver, spleen, or lymph nodes. Also called lymphoplasmacytic lymphoma.

A rare cancer of the lymph cells that causes the body to produce abnormal levels of plasma cells (plasmacytosis) and lymphocytes (lymphocytosis) in the bone marrow. Waldenstrom's macroglobulinemia may also cause a decrease in red blood cells (anemia) and enlargement of the liver (hepatomegaly), spleen (splenomegaly), or glands(adenopathy).