Overview of Feline 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 pet.
What to Watch For
Loss of appetite
Bleeding or bruising
Increased thirst and urination
Diagnosis of Leukemia in Cats
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 Cats
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 pet.
In-depth Information on Leukemia in Cats
The acute form of lymphocytic leukemia is called acute lymphoblastic leukemia, or ALL. 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 cats 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.
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.
Therapy and prognosis for the different types of leukemia are quite different. ALL tends to have a very poor prognosis, and affected animals often succumb to secondary infection. Although the cancer cells may respond to therapy, the presence of secondary complications often creates severe illness. In addition to being at risk for infection, these patients are often profoundly anemic, may develop life threatening bleeding disorders, and can even suffer from neurologic disease such as seizures and strokes. Unfortunately, pets with ALL often die within days to months of diagnosis. Animals with CLL, on the other hand, can do quite well and will often live several years with appropriate treatment. The mainstays of therapy are listed below.
Chemotherapy. Several different drugs are used in combination for the treatment of both ALL and CLL. Initially, this involves weekly visits to the veterinarian. The response to chemotherapy in patients with ALL is often disappointing. Most CLL patients do well with chemotherapy.
Blood transfusions. Because many of the animals with ALL are anemic at presentation, blood transfusions are often necessary to stabilize the pet. This requires careful monitoring and the availability of access to canine and feline blood products. Similar to human blood transfusions, the donor blood type must be compatible with the recipient’s blood type. Transfusions are often only available at specialty hospitals or emergency centers.
Antibiotics. Pets with ALL often have a low proportion of normal white blood cells, which work to fight infection. Because of this, they are at very high risk for bacterial infections that can be life threatening. Chemotherapy can also worsen the situation, as many drugs can lower the white blood cell count even further. Treatment with antibiotics is indicated to prevent overwhelming infection in these pets. If evidence of infection is already present, cultures of urine, blood, and possibly other fluids, is necessary to choose the appropriate antibiotic therapy.
Supportive care. In addition to the above therapies, severely ill pets require intravenous fluid therapy to correct dehydration and keep blood electrolyte levels balanced, as well as to help maintain normal blood pressure and kidney function. Nutrition is also an important component of therapy. Cancer patients lose weight rapidly and may not be able to get enough nutrients, especially if they are not eating, or they are experiencing gastrointestinal illness. Feeding tubes or intravenous feeding may be necessary to sustain patients. Intravenous feeding requires special catheter placement, and is only available at specialty hospitals with critical care facilities.
Follow-up Care for Cats with Leukemia
Optimal treatment for your pet requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your pet does not improve over the expected time frame. Administer all prescribed medications as directed. Alert your veterinarian if you are experiencing problems treating your pet.
Follow-up will include weekly evaluations of the CBC to monitor red and white blood cell counts and platelet levels. This is one important way to measure response to treatment. Additional bloodwork, such as biochemical profiles may also be needed, depending on the results of the original profile.
Just as important as the lab results, physical examination by your veterinarian on a weekly basis is imperative until the disease process is considered to be stable or in remission. Your veterinarian will monitor weight, body condition, and temperature and palpate lymph nodes and internal organs to assess their size.
Repeat x-rays or ultrasound exam may be indicated to track changes in organ size as well.
Once your pet is stable, less frequent exams will be needed, but close contact with your veterinarian is required for the life of your pet.
Monitor your pet at home for signs of lethargy, continued weight loss, anorexia, and general weakness. Learn how to check your pet’s temperature with a rectal thermometer and call the veterinarian if a fever is present. A temperature greater than 102.5 degrees Fahrenheit in a resting animal is abnormal. Remember that body temperature may rise with exercise and a warm environment.