Acute leukemia in dogs and cats is usually a cancer of young lymphocytes, a type of white blood cell. The lymphocytes involved are formed in the bone marrow and other lymphoid organs such as the liver and the spleen and other lymph nodes. Young lymphocytes are called blast cells. Often, these blast cells are released into the bloodstream, where they can be seen under the microscope. If blast cells are seen, then acute leukemia is diagnosed. Many different types of leukemia are possible, but we will deal primarily with the common lymphocytic leukemia in this article.

With leukemias, so many blast cells are released into the blood that the white-blood-cell count becomes very elevated. This is called leukocytosis. There are other reasons for leukocytosis besides leukemia. Leukemia differs from other forms of leukocytosis in that the white blood cells being produced are abnormal, and are primarily these immature blast cells. Lymphocytic leukemia may be acute or chronic. In general, acute leukemia is a more aggressive disease than chronic leukemia. Acute lymphocytic leukemia can be a dangerous, rapidly progressive cancer that can affect all ages of dogs and cats.

The cause of acute leukemia has not been identified in dogs. Some viruses of cats, birds and cattle can influence the development of leukemia in these species.

Patients with acute leukemia are typically sick, but often have vague clinical signs of weakness, anemia and lethargy. Enlargement of the spleen, lymph nodes and liver occurs in some animals. On blood counts, we see the large number of blast cells typical in leukemias. Because these blast cells are produced in the bone marrow, other cells produced in the bone marrow may be diminished, such as red blood cells, causing an anemia. Tests may be performed on these blast cells to identify the cancer cells and their stage of development.

Treatment of leukemia in dogs is often very satisfying, though it can be intensive and aggressive. Chemotherapy is the treatment of choice. Other supportive care may be needed, such as intravenous fluids, nutritional support, antibiotics and transfusions.

Many of these dogs and cats can live happy and long lives once remission is achieved. Talk to your veterinarian about this serious disease in dogs and cats.

Dr. Karsten Fostvedt is a veterinarian at St. Francis Pet Clinic in Ketchum.

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