Multiple myeloma ( + , "marrow" + "tumor"), is a
cancer of
plasma cells, a type of
white blood cell normally responsible for producing
antibodies. In multiple myeloma, collections of abnormal plasma cells accumulate in the
bone marrow, where they interfere with the production of normal blood cells. Most cases of multiple myeloma also feature the production of a
paraprotein—an abnormal antibody which can cause
kidney problems. Bone lesions and
hypercalcemia (high blood calcium levels) are also often encountered.