Overview of Canine Leukemia
Leukemia is a type of cancer that results from the proliferation of cancerous blood cells in the bone marrow. The cause of leukemia in dogs is unknown, although in humans, exposure to certain chemicals, treatment with chemotherapy drugs, and radiation therapy have all been implicated in causing leukemia.
Leukemia can be classified in many different ways, based on the specific type of blood cell which is involved. The most common form of leukemia seen in cats and dogs is lymphocytic leukemia, because of the involvement of lymphocytes, which are a type of white blood cell. Lymphocytic leukemia can be further broken down into acute (sudden onset) and chronic (long term illness) forms.
The impact of leukemia on your pet can vary with the form of the disease. The different forms have differing clinical presentations and each form carries a different prognosis for your dog.
What to Watch For
Signs of Leukemia in Dogs may include:
Loss of appetite
Bleeding or bruising
Increased thirst and urination
Diagnosis of Leukemia in Dogs
Complete history and physical exam
Complete blood count (CBC)
Chest radiographs (x-rays)
Abdominal radiographs or ultrasound exam
Bone marrow aspirate
Fine needle aspirate of abdominal organs or lymph nodes
Treatment of Leukemia in Dogs
Blood transfusions if patients are severely anemic (low red blood cell count)
Antibiotics to treat secondary infections
General supportive care
Home Care and Prevention
Give all medications as directed. Many patients with leukemia are predisposed to secondary infections due to a compromised immune system. Exposure to animals outside of the household should be minimized as much as possible.
There are no specific measures to prevent leukemia in your dog.
In-depth Information on Leukemia in Dogs
The acute form of lymphocytic leukemia is called acute lymphoblastic leukemia, or ALL. This form is more common in German shepherds and large breed dogs of any age. Pets with ALL are generally very ill, and begin to show clinical signs of illness fairly suddenly. Patients with ALL will often have a fever.
The chronic form of lymphocytic leukemia is called chronic lymphocytic leukemia, or CLL. This disease is usually seen in dogs older than 10 years, with no breed predisposition. Pets with CLL often have vague signs of illness that can be present for months to years before a diagnosis is made. The most common complaints include weight loss and lethargy, although the aforementioned signs can also be present.
Based on the clinical signs alone, leukemia can mimic a multitude of disease processes. The appropriate laboratory findings are crucial to making a diagnosis. However, other conditions that may cause similar clinical signs include:
Neoplasia (cancer), especially lymphoma. Lymphoma is another form cancer that is quite similar to leukemia and involves cancerous lymphocytes.
Autoimmine disease. Autoimmune or immune-mediated diseases occur when the body destroys its own cells. This often results in severe anemia and/or thrombocytopenia, which is a decrease in the number of platelets, cells that aid in blood clotting. Clinical signs of pale gums and bleeding or bruising can often be seen in autoimmune disease and leukemia.
Severe bacterial infection/sepsis. Sepsis is a disorder that occurs secondary to uncontrolled infection within the body. Sepsis can be associated with a variety of conditions, including ALL.
Severe inflammatory conditions such as pancreatitis or pneumonia. Inflammation of the pancreas, lungs, or other organs can also cause clinical signs similar to leukemia.
In-depth Information on Diagnosis
Complete history and physical exam. A thorough history is always important in establishing a list of possible diagnoses. A physical exam may reveal fever, enlarged abdominal organs, enlarged lymph nodes, and pale mucous membranes as in the gums, all of which may be commonly seen with leukemia, especially ALL.
Complete blood count. A CBC evaluates the red and white blood cells as well as the platelets. The red blood cells and platelets are often decreased in pets with leukemia. In cases of ALL, the white blood cell count may be high or low, with the presence of abnormally large lymphocytes, called blasts, in the blood. In cases of CLL, the lymphocyte count is abnormally high, but the cells appear normal in shape and size. Results of the CBC can be strongly suggestive of leukemia and this test is an imperative part of the work-up.
Reticulocyte count. Many pets with leukemia are anemic (low red blood cell count). The reticulocyte count measures immature red blood cells in circulation. Normally, the bone marrow responds to anemia by releasing reticulocytes, so this test is an evaluation of bone marrow function and also helps categorize the cause of the anemia.
A biochemical profile. This test evaluates blood sugar, blood proteins and electrolytes, as well as providing information about liver and kidney function. This helps to get an overall idea of systemic health, and may guide further diagnostic testing. Pets with leukemia often have cancer infiltrating the abdominal organs, which may lead to changes in the biochemical profile. Additionally, some pets have an elevation in their blood calcium level, which can be associated with several types of cancer. An elevation in the globulin level, which is a blood protein, can also be seen in pets with leukemia.
Urine analysis. Evaluation of the urine is part of a complete laboratory assessment and gives a better indication of kidney function than the biochemical profile alone.
Chest radiographs. X-rays of the chest are a good idea to look for evidence of spread of cancer to the lungs.
Abdominal x-rays or abdominal ultrasound exam. Imaging studies of the abdomen allow visualization of the abdominal organs to look for further evidence of cancer. It is not uncommon to find an enlarged liver and/or spleen in patients with leukemia.
Bone marrow aspirate. This is the definitive test for making a diagnosis of leukemia. Obtaining a sample of bone marrow involves placing a specialized needle within a bone and suctioning cells out. This procedure is usually done under heavy sedation or anesthesia, and is most commonly performed at specialty hospitals. Evaluation of an aspirate allows determination of the presence of cancer cells within the bone marrow.
Fine needle aspirate of abdominal organs or lymph nodes. Because leukemia is a disease of blood cells, the cancer often spreads throughout the body. Lymph nodes and abdominal organs may become enlarged when they are infiltrated with cancer cells. In cases when the organs are abnormally large, fine needle aspirates of these tissues will often confirm the suspicion of cancer in a given organ. A fine needle aspirate (FNA) involves placing a needle into an organ and applying suction to remove cells. Aspirates of abdominal organs are often performed with ultrasound guidance. If the FNA does not reveal a diagnosis, a surgical biopsy may be required to further analyze the tissue. The advantage of the FNA is that it can be done with minimal or no sedation in most animals, whereas a biopsy requires general anesthesia.