Multiple Myeloma (MM) is a cancer of plasma cells, which are specific types of B-lymphocytes (white blood cells) which produce antibodies as part of the body’s immune system. Multiple Myeloma is a relatively uncommon cancer and there is no gender or breed predilection in dogs. The average age at the time of diagnosis is 8-9 years.

What causes multiple myeloma?

The exact cause of cancer and MM is unknown in dogs. In people damage to DNA or chromosomes are being investigated as possible causes.

Common signs of this cancer

• Affected dogs can exhibit signs of lethargy, weakness, lameness, bone pain (due to the destruction of bone caused by the malignant plasma cells), hemorrhage (e.g, petechiae on mucous membranes, gingival bleeding, or bleeding from the nose), polyuria / polydypsia (increased urination and thirst), and/or neurologic deficits. Other presenting signs of disease may include hypertension (high blood pressure), ophthalmic (eye) abnormalities, neurologic dysfunction (including seizures).
• The clinical signs of multiple myeloma are highly variable and may affect multiple organ systems. The presentation of a patient with multiple myeloma will depend on the type of neoplastic cell, type of immunoglobulin (antibody) produced, location of lesions, and severity of growth and infiltration.
• Clinical signs and symptoms may be present for up to 1 year before a definitive diagnosis of multiple myeloma is made. Patients can also present with recurrent infections, non-regenerative anemia, hypercalcemia, pathologic bone fractures, and/or seizures. Complications secondary to multiple myeloma may include kidney failure, infections secondary to immunosuppression, clotting disorders, chronic anemia, cardiac insufficiency, and neurologic dysfunctions.

How is multiple myeloma diagnosed?

Diagnosis of multiple myeloma in dogs requires at least two of the following criteria:

1.  Radiographic evidence of osteolysis (bone destruction)

2.  >20% plasma cells in bone marrow aspiration or biopsies

3.  Monoclonal gammopathy on serum protein electrophoresis

4.  Bence-Jones proteinuria—a particular type of protein in urine

     Radiographic Evidence of Osteolysis

• Areas of bony destruction (osteolysis) may be seen in ~40% of dogs suffering from multiple myeloma (in contrast, osteolytic lesions rarely are seen in cats).The bones most commonly involved in canine multiple myeloma include the spine, pelvis, ribs, skull, and proximal extremities. In addition, malignant plasma cell tumors present in the bone marrow are often osteolytic.
• Survey radiographs may reveal focal, multifocal, or diffuse osteoporosis-type lesions. Clinically, the patient may present with pathologic fractures, rear limb lameness or paresis, or bone pain. 

     Bone Marrow Aspirates with > 20% Plasma Cells

• Bone marrow analysis is an essential procedure when multiple myeloma is suspected. Diagnosis is facilitated by taking aspiration and core marrow biopsies from areas of bone destruction (osteolysis). Cytologic evaluation of the bone marrow should reveal that plasma cells constitute > 20% of all nucleated cells in animals with MM.

     Hyperproteinemia with Monoclonal Gammopathy

• Hyperproteinemia (elevated protein) and an elevated globulin (a type of protein found in the blood) level can be easily detected on routine bloodwork.  Serum electrophoresis should be performed on all patients that present with an elevated globulin level and signs suggestive of multiple myeloma. 

How is multiple myeloma treated?

• Goals of treatment include decreasing tumor cell numbers as well as treating the secondary systemic effects.
• Chemotherapy is effective at reducing tumor cell numbers, decreasing bone pain, aiding in bone healing, and decreasing serum immunoglobulin levels.
• Chemotherapy can increase both the quality and quantity of life.
• The chemotherapy protocol of choice (for dogs) consists of oral Melphalan (Alkeran) and prednisone—in cats we use oral Chlorambucil (Leukeran) and prednisone. Other chemotherapy agents such as Cyclophosphamide can also be used. If advanced myeloma is diagnosed or if a patient becomes resistant to oral chemotherapy, intravenous chemotherapy may be used. The animals handle these therapies extremely well.
• Radiation therapy also can be used with relatively good results in cases of isolated plasma cell tumors and can be very effective in treating the bone pain caused by this disease.
• Supportive therapy is essential in animals with multiple myeloma to relieve immediate clinical problems. 

What is the prognosis of dogs with this cancer?

Median survival times of 18 months or longer can be achieved with chemotherapy and supportive care.

Multiple Myeloma in Cats

• MM is a rare diagnosis in cats
• The average age of diagnosis is 12.5 years
• There is a possible gender predilection for males
• There is a breed predilection for domestic short hairs
• Imaging commonly reveals enlarged liver, enlarged spleen and enlarged heart and kidneys
• Treatment with chemotherapy results in median survival times of around 1 year 

What is on the horizon for this disease?

The use of a new class of drugs, called proteosome inhibitors has shown great promise in people. In addition, drugs like thalidomide have been working effectively in people for a number of years.