Leukemia In Dogs

The Many Types of Leukemia in Dogs

Leukemia is a type of cancer affecting humans and animals in which white blood cells essentially go into overdrive. “Leuk” means white, and “emia” means blood. Leukemia in dogs is rare, thankfully.

In a healthy body, white blood cells act as part of our immune defense system, fighting infection and injury and supporting the body in times of stress. In leukemia, the bloodstream is flooded with so many cancerous white blood cells that the body stops producing enough of the other important cells needed to function properly.¹

Dogs can have many types of leukemia, and the terms can be confusing, so we’ll break it down for you.

Chronic or Acute? Lymphoid or Myeloid?

Leukemia is categorized as either chronic or acute:

• Acute means “quick onset of symptoms.” Acute leukemia typically involves immature cells in the bone marrow.
• Chronic means “slow onset of symptoms.” Chronic leukemia typically involves mature lymphocytes in the bone marrow or circulating throughout the body.

It’s also categorized as either lymphoid or myeloid:

• Lymphoid means the cancerous cells were supposed to become lymphocytes, a specific type of white blood cell.
• Myeloid means the cancerous cells were supposed to become red blood cells and non-lymphocyte white blood cells.⁶

Combining these terms, there are five main leukemias described in dogs:⁴

• Chronic lymphocytic leukemia (CLL)
• Chronic myeloid leukemia (CML)
• Acute lymphoblastic leukemia (ALL)
• Acute myeloid leukemia (AML)
• Acute undifferentiated leukemia (AUL), meaning it is uncertain where it started

In general, dogs with chronic leukemia progress gradually and can have a longer survival time, while those with acute leukemia become sick quickly with a rapid progression and poor prognosis.²

Type of Lymphocyte

To make it even more complicated, Acute Lymphoblastic Leukemia (ALL) and Chronic Lymphocytic Leukemia (CLL) can be further classified by what type of lymphocyte the original cell was: B-cell, T-cell, or natural killer (NK) cell.⁶

Studying Dogs and Humans with Leukemia

Since leukemia affects humans and dogs, studies involving one species can benefit the other. Comparative oncology is a field where researchers use studies from one species and apply them to develop studies in another.

The National Cancer Institute has used comparative oncology to examine the most common blood cancers (leukemia and lymphoma) and other cancer types. The more research and studies performed on both species, the more likely new, successful treatment strategies will be developed.³

Stats and Facts

• In dogs, chronic Myeloid Leukemia (CML) and Acute Undifferentiated Leukemia (AUL) are both rare leukemias.⁴
• Leukemia is relatively uncommon in dogs.
• Acute leukemias are more common than chronic.⁷
• In acute leukemia, the cancerous white blood cells are immature and proliferate more rapidly. In chronic leukemia, the white blood cells are more mature, and progression typically occurs more slowly.⁵
• Lymphoid leukemias are believed to be more common than myeloid leukemias.⁶
• Lymphoid leukemia accounts for about 10% of blood cancers in dogs.⁶

Causes of Leukemia in Dogs

We don’t know the “one cause” of why some dogs develop leukemia.

Exposure to radiation and carcinogens such as benzene and phenylbutazone have been implicated in people. Specific viruses can lead to leukemia in cats, cattle, and birds. However, these causes have not yet been shown in dogs.¹

Risk Factors

Leukemia can occur in any breed or age of dog.

Golden Retrievers and German Shepherds are two breeds that possibly have an increased risk of acute leukemia. Acute leukemia may also be more common in male, middle-aged dogs.⁵

Other breeds that possibly have an increased risk of chronic leukemia: Pit Bulls, English Bulldogs, Boxers, Shih Tzus, Jack Russell Terriers, Dachshunds, and Cocker Spaniels. Chronic leukemia may also be more common in older dogs of either sex.^3,7,8

Symptoms

Dogs with acute leukemia are often quite sick. Common symptoms of dogs with acute leukemia include:

• Lethargy
• Decreased appetite
• Weight loss
• Vomiting
• Diarrhea

Less common symptoms of acute leukemia in dogs include:⁶

• Fever
• Labored breathing
• Altered neurological status (cognitive problems)
• Increased thirst and urination

If your dog with leukemia didn’t have any of these symptoms, that’s quite common. Many dogs with chronic leukemia do not have any symptoms at the time of diagnosis. Their veterinarian usually finds it in routine wellness blood screening.

When a dog with chronic leukemia does feel sick, the symptoms are usually vague and non-specific. These symptoms include:⁶

• Lethargy
• Reduced appetite
• Intermittent vomiting
• Increased thirst and urination

Some dogs may have swollen or prominent lymph nodes (this can happen with either acute or chronic leukemia). However, if lymph nodes are enlarged, they are typically not as enlarged as in dogs with lymphoma.^6,9

Diagnosis of Canine Leukemia Can Be Tricky

Leukemia can have similar physical exam and blood work findings as other diseases, including lymphoma and the tick-borne disease Ehrlichia. This means leukemia is sometimes misdiagnosed at first. More tests specific to leukemia are needed to avoid misdiagnosis of canine leukemia.

Correctly identifying the type of leukemia helps determine prognosis and treatment plans.

Your dog’s veterinarian or veterinary oncologist may recommend some or all of these tests:

• Bloodwork, especially the Complete Blood Count — a standard blood panel that looks at red blood cells, white blood cells, and platelets.
  • A normal lymphocyte count is less than 3,500 cells per microliter. This count may range from 6,000 to over 100,000 cells per microliter in dogs with lymphocytic leukemia.⁵
  • Dogs with myeloid leukemia may have a normal white blood cell count.⁵
• Blood Smears. This test involves gently wiping a drop of your dog’s blood across a slide, so that the veterinary pathologist can look at the individual blood cells on a microscope. This veterinary specialist can evaluate the maturity of the blood cells, screen for signs of malignancy, and look for abnormal cell numbers.⁵
• Immunophenotyping. This process uses antibodies to identify the type of cell in a sample, which helps identify the exact type of leukemia your dog has. Immunophenotyping can be done with a blood sample from your dog’s vein or from a fine needle aspirate.¹⁰
• Polymerase Chain Reaction (PCR). This test uses DNA to differentiate leukemia from other reasons for an increased lymphocyte count.⁶
• Bone Marrow Aspirate. This test involves using a very large needle to get a sample of the bone marrow to submit for testing and evaluation. It is invasive and painful and is generally only done if other tests have not yielded a diagnosis.⁶
• Imaging. Radiographs (x-rays) and/or abdominal ultrasound may be done to check the lymph nodes, lungs, and other organs for evidence of disease.⁸

Prognosis and Staging

Staging is the process of determining the extent of cancer in the body. It can help determine treatment plans and refine your dog’s prognosis. There is no true, well-developed clinical staging system for lymphoid leukemia in dogs. We hope that one is developed in the future.

For now, the following guidelines may help you orient yourself:

The Prognosis for Acute Leukemias

Acute leukemias are more aggressive, infiltrative, and have a rapid disease course. The reported survival time in dogs is days to months (1-120 days).^10,11

Dogs with a normal red blood cell count and normal neutrophil (white blood cell that helps fight off infection) count at time of diagnosis had a better overall prognosis and increased survival time.¹¹

The Prognosis for Chronic Leukemias

For chronic leukemias there is wide variability in reported survival times.

With successful treatment, some dogs can survive years with chronic leukemia.

Without treatment, survival times depend on whether your dog had symptoms and how abnormal his bloodwork was at the time of diagnosis.

Treatment

Let’s get the bad news out of the way: in general, leukemia in dogs cannot be cured, but it can be managed with a focus on life quality.

For example, dogs with chronic lymphocytic leukemia (CLL) usually don’t go into remission. However, they can live with chronic leukemia for a long time – years in some cases. That said, even mild cases that respond well to treatment still progress, ever so slowly. Eventually, leukemia usually wins.

Dogs with acute leukemia usually have rapidly progressing disease, no matter what treatment they are given.

Even so, dogs with either acute or chronic leukemia who are showing symptoms of illness can be helped with supportive therapy. These kinds of treatments include:⁶

• broad-spectrum antibiotics to prevent sepsis (an infection in the bloodstream)
• intravenous fluids to correct dehydration
• nutritional support
• blood transfusions

So what other treatments might your veterinarian suggest? Because leukemia is systemic — it is everywhere — the most promising is chemotherapy.

Chemotherapy

There is much to learn about the successful treatment of acute leukemia in dogs. There are not a lot of dogs that get it, the disease is very aggressive, and the dogs who get it are typically very sick when diagnosed,¹¹ so few veterinary oncologists have experience treating it.

But we do know aggressive chemotherapy is typically needed.

Chemotherapy agents that have been used for acute leukemias include:

• Vincristine
• Prednisone
• Cytosine arabinoside
• Cyclophosphamide
• L-asparaginase¹¹
• Prednisone-based multi-drug chemotherapy protocols such as CHOP, typically used in lymphoma¹³
• Doxorubicin, usually as a rescue agent for Acute Lymphoblastic Leukemia (ALL)⁶

Cytosine arabinoside in combination with an anthracycline leads to long-term overall survival in humans with acute leukemias. This approach may be promising for dogs with acute leukemia.¹¹

First-line treatment options typically used for chronic leukemias include:

• Corticosteroids such as prednisone
• Chlorambucil
• Cyclophosphamide
• L-asparaginase

Additional chemotherapeutic drugs may be considered if a dog is poorly responsive to first-line therapy, or if ‘malignant transformation’ (sudden increase in progression) occurs.

Boxers generally have a poor prognosis. For other dogs, treatment with corticosteroids and chlorambucil often provided longer survival times.⁸

Chemotherapy rarely results in tumor lysis syndrome, a very serious and life-threatening complication. Tumor lysis syndrome occurs when a large number of cancer cells die and flood the body with debris. If it happens, it is usually during the very first chemotherapy appointment. Symptoms include vomiting, diarrhea, and lethargy, and death can occur within hours after chemotherapy is started. Hospitalization and aggressive intravenous fluids are needed to save dogs with tumor lysis syndrome.⁶ The veterinarian or oncologist will carefully monitor your dog during and after administering chemotherapy, especially on the first visit, to ensure they are well before discharging them.

Radiation

Radiation to the whole body is a part of leukemia treatment in certain specific situations:

• As part of the procedure for a bone marrow or peripheral blood stem cell transplant¹⁴
• When leukemia has spread to the brain and spinal fluid or the testicles
• To relieve severe bone pain¹⁵

Immunotherapy

Immunotherapy is a promising option for treating leukemia in dogs. However, most treatments are still considered experimental.

Stem cell transplants potentially cure various blood diseases (including blood cell cancer) in people. Unfortunately, a cure — even with aggressive transplantation — is not anticipated in dogs.^9,16,17

One promising therapy uses Chimeric Antigen Receptor (CAR) cells specially engineered to target and kill cancer cells. Chimeric Antigen Receptor (CAR) T-cells targeting the CD19 receptor on leukemia and lymphoma cells have been quite helpful in humans. The FDA has even approved the first treatment of this type for CD19-positive Acute Lymphoblastic Leukemia (ALL) in humans. We don’t (yet) know if the same tumor-associated antigens are usable targets in canine leukemia.¹⁸

Dogs represent a good model for cancer immunotherapy research in humans.¹⁹ This suggests there will continue to be studies in both species, hopefully leading to more treatment options in the future.

Surgery

Surgery is not considered a treatment for chronic or acute canine leukemia. Unfortunately, cancerous leukemia cells are spread widely throughout the bone marrow and blood. There is no one tumor site to cut out: they are everywhere. That’s why surgery is not a cure.¹²

Vaccine

Vaccines to treat acute leukemia in humans are currently being tested. There are no vaccines available to dogs at this time.²⁰

Diet

There are no specific dietary recommendations for dogs with leukemia, but general dietary advice might be considered.

Supplements

Several supplements have been studied in vitro (tested outside of a living body) in blood cell cancer lines.

• Quercetin has been examined in blood cancers²¹ and its use has been reported in conjunction with chemotherapy in Chronic Lymphocytic Leukemia (CLL).²²
• Beta glucans has shown promise in patients with Acute Myeloid Leukemia (AML).²³
• Curcumin is generally considered to have anticancer, antioxidant, anti-inflammatory, immune system, and liver protectant properties.²⁴
• Moringa oleifera extracts have been suggested to have anti-leukemic effects.²⁵

Integrative Therapies

Although there is generally a lack of “hard” evidence for integrative therapies, a study showed that traditional Chinese medicine may be helpful when combined with conventional Western medicine to treat patients with leukemia. Together they may positively impact survival in these patients.²⁶

The Final Stages of Leukemia in Dogs

The prognosis for dogs with acute leukemia is poor, and many dogs are very sick at diagnosis. For these reasons, many owners consider euthanasia early in the process. Once a dog reaches the final stages of acute leukemia, symptoms are severe and include respiratory problems, fever, and systemic infections (sepsis).^10,28

On the other hand, dogs with chronic leukemia can survive for months to years with the disease, often with good life quality. They will eventually start to feel very sick as the disease progresses.

One possible final stage in canine chronic leukemia is the development of large cell lymphoma (cancer of the lymph nodes, called Richter’s syndrome in humans).⁶ Many dogs are euthanized when they feel so sick that it affects their quality of life.

Prevention Strategies

There is no known way to prevent leukemia in dogs. Prevention of leukemia in people may be possible by avoiding exposure to certain risk factors such as smoking, benzene exposure, and high-dose ionizing radiation.²⁹