Multiple myeloma is a tumor involving blood cells called plasma cells. Plasma cell tumors often grow in the bone marrow cavities. The growth of these tumors can cause a replacement of other cells in the bone marrow, with a resultant decrease in the production of other blood cells. Normally plasma cells produce a protein, a type of antibody, that circulates in the blood. The tumor produces this protein in amounts that can thicken the blood and slow the circulation, which can affect kidney function.
