Canine Leukemia

What is Leukemia?

Leukemia means "white blood" and, as a disease, refers to a condition where the number of white blood cells in the bloodstream or the bone marrow is increasing in an abnormal rate.

It is a result of genetic mutation that alters the structure of the bone marrow, causing it to over-produce cancerous cells and under-produce other healthy blood cells that a dog needs.

Forms and Stages of Canine Leukemia

There are several forms of leukemia.

Canine leukemia is classified according to the type of cells involved and the developmental stage of the cancerous cells that are causing the disease.

Forms of Leukemia

• Lymphocytic Leukemia: This form of leukemia involves lymph node cells.
• Myelogenous Leukemia: This form originates from the bone marrow.

Dogs are more prone to the development of lymphocytic leukemia.

Stages of Canine Leukemia

Both of these two forms of leukemia (lymphocytic leukemia and myelogenous leukemia) may either be acute or chronic, depending on how mature the cancer cells are.

• Acute Leukemia: This stage refers to the rapid and sudden increase in the number of immature blood cells (blood cells that are in their early stages of development).

  The increase of these immature cancerous blood cells is so dramatic that it hinders the production of other healthy blood cells, posing an immediate threat to the dog patient's life.

• Chronic Leukemia: This stage refers to the abnormal increase in the number of more developed, mature blood cells. The increase is not sudden but rather is a build-up over months or even years. Chronic leukemia occurs more frequently in older dogs.

As a general rule, the acute forms of canine leukemia is more malignant than the chronic forms.

Acute Lymphocytic Leukemia in Dogs

As mentioned above, acute leukemia acts more malignantly than chronic leukemia. Making use of the circulation system, the cancerous blood cells can easily spread to other parts of the body such as the liver and the spleen.

As well, since the bone marrow is so preoccupied with making these cancerous cells, there is an alarming lack of other healthy blood cells that a dog needs.

This acute form of canine leukemia usually affect dogs who are six years of age or older, but younger dogs (under 4 years of age) can also be affected.

Signs of Acute Leukemia

Dogs with acute leukemia generally show some of the following signs:

• Tendency to bleed or bruise easily (This is due to the high number of immature blood cells and lack of blood platelets that are responsible for blood clotting.)
• A dysfunctional immune system resulting in recurrent infections and delay in healing time
• Appetite loss
• Weight loss
• Lethargy
• Pale gums
• Diarrhea
• Lameness

Treatment for Acute Leukemia

Dogs with acute leukemia may require chemotherapy in order to stop the growth of the cancerous blood cells.

However, even with aggressive chemotherapy, only about 30 percent of dog patients can have remission. In many cases, the dogs' immune systems are so weak and dysfunctional as a result of the cancer that the chemotherapy drugs cause them to succumb to secondary diseases.

Very often, more drugs (e.g. antibiotics) are needed to treat the secondary diseases. In addition to chemotherapy, many dogs need blood transfusions because of the severe anemia caused by the leukemia.

Without any type of treatment, most dog patients with acute leukemia die within a few weeks.

Chronic Lymphocytic Leukemia in Dogs

While acute leukemia is aggressive and can develop very rapidly, the development of chronic leukemia is much slower (months or even years).

Chronic leukemia is usually diagnosed in older dogs (10 to 12 years of age).

Many dogs (about 50%) with the chronic form of leukemia do not have any signs or symptoms.

Since chronic leukemia in dogs is not as aggressive as the acute form, it can be controlled effectively by chemotherapy. What's more, even without any chemo treatment, a dog with chronic leukemia can live up to two years after diagnosis.

Causes of Canine Leukemia

There are no known causes of leukemia, although many veterinarians believe that genetics may be a factor, as some breeds are more prone to the disease.

Leukemia may also result from constant exposure to radiation, certain chemicals and viruses.

Diagnosis of Canine Leukemia

Appropriate laboratory finding are critical to diagnosis of leukemia.

The reason is, some of the symptoms of leukemia are rather indistinct and are similar to those of many other diseases (e.g. severe bacterial infection; severe inflammatory conditions such as pancreatitis; autoimmune disease, lymphoma).

Diagnosis of dog leukemia include the following tests:

• Complete blood count
• Biochemical profile
• Urinalysis
• Chest x-rays
• Abdominal ultrasound and/or x-rays
• Bone marrow aspirate
• Fine needle aspirate of lymph nodes and/or abdominal organs

References
Eldredge, et al. Dog Owner's Home Veterinary Handbook 4th edition (Wiley Publishing, 2007).
S. Messonnier, The Natural Vet's Guide to Preventing and Treating Cancer in Dogs (New World Library, 2006).