Multiple myeloma in cats

Last Modified: February 16, 2003


Dear OncoLink "Ask The Experts,"
Our 15 1/2 year old cat recently has been diagnosed with Multiple Myeloma. Can you tell me a little about the diagnosis and possible treatments? 


Lili Duda, VMD, Section Editor of the OncoLink Veterinary Oncology Menu, responds:

Multiple myeloma is an uncommon cancer of a type of white blood cell known as a plasma cell. These white blood cells are the ones that produce antibodies, which fight off infection. In order to diagnose multiple myeloma, at least 2 of four criteria must be met:

  1. Evidence of bone involvement, which is diagnosed by taking X-rays of the entire patient and looking for areas of "bony lysis" which are circular areas within bone that have been damaged by the tumor.
  2. Evidence of a type of protein called "Bence-Jones" proteins in the urine, which are pieces of antibody proteins produced by the cancer cell. This is diagnosed by sending a urine sample to a laboratory.
  3. Evidence of a "monoclonal spike" which is a large amount of a specific globulin produced by the cancer cells. This is diagnosed by sending a blood sample to a laboratory where they perform a test called "electrophoresis" which breaks down the blood protein into all the individual types of globulin to see what the proportions are.
  4. Evidence of an increased number of plasma cells in the bone marrow, which is diagnosed by doing a bone marrow aspirate (which usually just required local anesthesia and maybe some mild sedation) and sending the cells to a laboratory where they place the sample on slides and look for the plasma cells under the microscope.

Many of the clinical signs of multiple myeloma are caused by the increased amount of globulin protein in the blood. This globulin can cause the blood to become very thick and viscous, which can cause heart problems because it has to work so much harder to pump the blood, and kidney problems because the protein can clog up the kidneys. It can also cause decrease in immune function as well as bone pain. Treatment is aimed at reducing the number of cancer cells and decreasing the amount of globulins in the blood. Chemotherapy is the initial approach, which consists of high dose prednisone (which is chemotherapeutic against cancerous plasma cells) and another chemotherapy drug called melphalan. Specific organ problems are treated symptomatically. While multiple myeloma is probably the most common cause of elevated globulins in the older cat, there are other causes, such as lymphosarcoma or leukemia (which is also a treatable cancer) and a variety of infectious diseases.