Facts In a healthy body, the white blood cells (leukocytes) are an essential part of the dog’s immune system. They are produced in the bone marrow and work to defend the dog’s body against foreign invaders and infectious diseases. There are several different types of white blood cells (eosinophils, lymphocytes, platelets, basophils, monocytes, and neturophils), each with its own role. Leukemia, a form of cancer, is a disease wherein the white blood cells proliferate abnormally in the blood and bone marrow. Being malignant, leukemia often spreads to other parts of the body. Leukemia can be chronic or acute. The chronic form involves an abnormal proliferation of mature white blood cells (WBC), while the acute form involves the abnormal growth of immature, cancerous leukocytes. Leukemia is classified according to the type of white blood cells that are involved. Within the bone marrow, leukemia cells multiply to the point of crowding out normal, healthy WBCs and bone marrow cells. Eventually it spills out into the dog’s circulatory system, which leads to a reduced number of healthy white and red blood cells in circulation. Because the dog’s white blood cells can’t properly do their job, the immune system is impaired. This leads to illness, infections, and other problems. The cancerous WBCs usually accumulate in the gastrointestinal tract, central nervous system, spleen, kidneys, liver, and lymph nodes, which disrupts their regular function.
Causes The exact causes of leukemia are unknown. Some theories about what make a dog develop this disease are exposure to toxins or radiation, infection, or genetic factors.
Prevention Preventing leukemia is impossible, because no one knows for sure what causes it.
Symptoms The symptoms for leukemia can be very vague and are similar to those caused by other diseases. A dog may show one or more of these symptoms: vomiting, weight loss, fever, lack of appetite, abdominal distension, general malaise, weakness, diarrhea, abdominal pain, lethargy, elevated heart rate, difficulty breathing, polydipsia (increased water intake and thirst), elevated respiratory rate, lameness, enlarged spleen, polyuria (increased volume and frequency of urination), bruises, enlarged liver, bleeding disorders, enlarged lymph nodes, dehydration, and pale mucous membranes.
Dogs at Risk Chronic leukemia is less common than the acute form. It appears more often in males and older dogs. Acute leukemia is more prevalent in dogs around five to six years of age. Dogs of any breed, age, or gender can develop leukemia.
Testing and Diagnosis Leukemia is suspected after a routine blood test shows unusually high numbers of white blood cells in the sample. This blood test may be done to help determine what is causing a dog’s symptoms, or may be a routine yearly checkup on a dog with no illness. To definitively diagnose leukemia, a core biopsy and/or bone marrow aspiration is performed. This is done from a sample on the iliac crest on medium and large dogs; in small dogs, a sample is taken from the trochanteric fossa area of the hip. The dog is sedated for these tests, because they are quite painful. Other tests include needle aspiration of the liver, spleen, or lymph node to check for cancerous leukocytes; and chest and abdominal x-rays and/or ultrasounds to look for enlarged organs.
Treatment and Prognosis The treatment goal for leukemia is to put the dog into remission, which means to halt or reduce the signs of the illness. Vets do this by attempting to restore the dog’s bone marrow production to normal, by providing supportive care to the patient (which includes relieving discomfort), and by attempting to eradicate the cancerous WBCs. Specialty veterinarians, called veterinarian oncologists, are the best choice for treatment and advice. Cases of acute leukemia require aggressive, supportive inpatient care, which may include some or all of the following: IV therapy, blood transfusions and forced nutrition if necessary, and broad-spectrum antibiotics. Dogs with chronic leukemia usually are prescribed antibiotics as well. Treatment for leukemia includes chemotherapy to kill most of – or many of – the malignant cells. Unfortunately, chemo usually causes diarrhea, nausea, vomiting, and general malaise because the drugs also affect the rapidly-dividing cells in the lining of the gastrointestinal tract. Dogs on chemo are sometimes hospitalized for constant care. The prognosis for dogs diagnosed with the acute form of leukemia is poor, although statistics may be inaccurate due to the high number of dogs that are euthanized instead of treated upon diagnosis. Many dogs diagnosed are far along in the disease since it progresses so quickly, and even the most aggressive treatment protocols sometimes have no effect. Survival time is sometimes as short as four weeks following a diagnosis. Dogs diagnosed with chronic, slow-onset leukemia have better chances of surviving longer – up to six years, in some cases.