Bone Marrow Cancer in Dogs

Every year many dogs are diagnosed with cancer and sadly this is the major cause of death in dogs over 10 years old. Myeloma is a type of cancer affecting white blood cells called plasma or B cells and because those originate directly from the bone marrow, this type of cancer is also known as “bone marrow cancer.” Dogs affected by Myeloma have an overproduction of immunoglobulins (antibodies) which are produced by the continuously dividing plasma cells. Myeloma is not very common in dogs and it accounts for less than 1% of cancer cases; however symptoms can be very severe from bleeding, osteoporosis, renal dysfunction, loss of eyesight and neurological complications. Often the animal’s death happens from the occurrence of secondary infections.Multiple myeloma is an uncommon cancer that is derived from a clonal population of cancerous (malignant) plasma cells in the bone marrow. Although myeloma is not currently curable, it's relatively uncommon in canines and has successful treatment options. If your dog is suspected of having Multiple Myeloma, a Veterinary Oncologist would best manage the definitive diagnosis and treatment of your dog.

Symptoms can vary and affect multiple organs and tissues. Dogs affected by Myeloma show signs of general discomfort including weakness, lethargy, apathy and loss of appetite. Clinical symptoms are caused by the abnormal presence of immunoglobulins and plasma cells in the bones and other tissues and they include:

• Bone lesions, especially long bones of the limbs, back bones, ribs and skull.
• Severe bleeding and anemia.
• Blood hyperviscosity.
• Cardiac complications.
• Renal failure.
• Severe immunodeficiency and increased susceptibility to infections.
• Neurological issues such as dementia.

Types

There is only one type of Myeloma, although it can be named differently such as multiple Myeloma (MM) or bone marrow cancer.

The causes of Myeloma are still unknown; the cancer generally appears between 8 and 9 years of age and certain breeds have higher predisposition such as German Shepherds, Boxers and Golden Retrievers. No correlation between the onsets in male or female dogs has been reported. There is a possibility that Myeloma is triggered by genetic causes; some studies indicate that the misregulation and the functional disruption of a protein called Cyclin D can be responsible for the disease. In humans, plasma cell cancer is often linked to environmental factors, such as pollution by chemical and toxin agents and this cannot be completely excluded as risk factor triggering the cancer in dogs.

Similarly, to other diseases, it is recommended that veterinarians run a thorough physical examination of the animal alongside with more specific biological analysis, this will help to deliver a clear and an accurate diagnosis. In a dog the presence of Myeloma is confirmed when at least two of the following signs are detected.

• High concentration of immunoglobulins (antibodies-paraproteins) in the blood.
• Bone lesions and areas of severe bone loss.
• A value >5% of neoplastic cells in the bone marrow.
• A value comprises between 10% to 20% of plasma cells in the bone marrow.
• Bence Jones immunoglobulins in the urine.

Thus an accurate diagnosis should include:

• Blood count and a complete blood cell profile.
• Assessment of blood coagulation and serum viscosity.
• Urine sampling including detection of Bence Jones immunoglobulins.
• Radiographic and ultrasound analysis to look at bone density, presence of bone lesions and state of abdominal organs.
• Biopsy of osteolytic lesions.
• Analysis of bone marrow aspirate.

Pet owners are called to strictly observe their dog’s behavior with specific attention if there are any signs of weakness and tiredness, or if the animal bleeds or if thirstier and urinates often.

Treatments for MM target the cancer itself (primary treatments) or they are more directed to all secondary effects caused by the cancer (secondary treatments).

Primary treatments

• Chemotherapy is for sure the treatment of choice for MM and in the majority of cases it has successfully reduced the cancer size and symptoms, however this cannot be considered as a complete cure. Melphalan is the most recommended chemotherapy agent that works by blocking all cell replication including cancer cells. Melphalan is an oral drug and it is often prescribed together with Prednisolone (antinflammatory). The treatment duration varies between 5 to 21 days and common side effects are immunosuppression (myelosuppression) and a reduction in blood clotting (thrombocytopenia). Cyclophosphamide and Chlorambucil are alternatives to Melphalan with a similar mechanism of action. If chemotherapy is successful it can takes up to 6 weeks to see an improvement of the dog’s clinical signs and biological values.
• Radio therapy is another primary treatment although it is less common than chemotherapy and it can only treat a specific area.

Secondary treatments

• Aggressive fluid therapy is employed for renal failure and hypercalcemia; as long-term treatment is used to ensure an adequate hydration to the dog.
• Antibiotics are mainly used to treat secondary infections.
• Orthopedic surgery to repair fracture bones.

Novel therapeutic approaches such as stem cells transplant and compounds used to treat other diseases such as Thalidomide and Toceranib phosphate are now undergoing clinical studies.

In the majority of cases chemotherapy greatly improves dog conditions and can result in long time remissions. During the therapy a complete blood cell count is necessary every two weeks together with protein analysis to strictly monitor effects of chemotherapy agent on bone marrow. Once values are back to normal levels blood analysis can be performed monthly together with bone density and X-rays.

Unfortunately chemotherapy and all secondary treatment of MM do not represent the cure, however a good improvement of the dog’s quality of life can often be achieved; extraordinary results have been shown from a study conducted on 60 animals treated with chemotherapy where 43% reported a complete remission, 49% a partial remission and only the 8% did not responded to the therapy. Median survival of a dog treated with chemotherapy is of 540 days compared to dog treated with Prednisolone only.