Multiple myeloma (myelo- + -oma, "marrow" + "tumor"), also known as plasma cell myeloma, myelomatosis, or Kahler's disease (after Otto Kahler), 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.