Multiple myeloma (plasma cell neoplasm) is a rare type of cancer that results in the uncontrolled production of one type of white blood cell (plasma cell) in the bone marrow. The cancer cells can crowd out normal blood cells, causing a reduction in red blood cells (anemia).
The overproduction of plasma cells causes an increase in antibodies. The plasma cells also may cause the bone to break down. The plasma cells can collect in the bone to make small tumors called plasmacytomas.