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Understanding Leukemia

White blood cells are an important part of the immune system in both animals and humans. When these cells, which come in various types, begin to divide out of control in the blood or bone marrow, they become the cancer known as leukemia. This type of cancer can be either acute or chronic.

Acute

Acute cancer cells are immature, while chronic cancerous cells are more mature. The acute cells tend to be more aggressive because they are more readily able to divide and do so at a rapid rate. In this type of cancer, the bone marrow is unable to produce healthy cells due to the presence of the cancerous cells overcrowding the marrow. It also tends to have poor responses to chemotherapy. A typical treatment may include injectable chemotherapy but has very abbreviated survival times of a couple of months.

Dogs with acute leukemia tend to present with a variety of clinical signs; however, they are typically sick. Signs include lethargy, decreased appetite, vomiting, and an elevated temperature. These signs, however, are nonspecific and do not directly indicate leukemia.

In cats, this type of cancer is unusual. Before the availability of the feline leukemia virus (FeLV) vaccination, acute leukemia was much more common. FeLV infections can be progressive (high level of virus and antigen present, infectious), regressive (low level of antigen and provirus, non-infectious), or abortive (where the patient’s immune system is able to eradicate the virus). Typically, FeLV positive cats that develop acute leukemia have a progressive infection.

Diagnosis

Bloodwork can reveal common abnormalities such as high lymphocyte counts, low red blood cells, low ‘good’ white blood cells, and low platelets. Once the elevated white blood cells have been discovered, a test called flow cytometry may be recommended. This test involves taking a sample of blood and looking for specific markers on the cells to identify the leukemia. Other ‘staging’ tests, such as x-rays or ultrasound, may be recommended to determine if the cancer has spread to other parts of the body. In some situations, an aspirate of the bone marrow may be recommended to obtain a more definitive diagnosis.

Once a diagnosis is obtained, treatment is primarily made up of injectable chemotherapy. There are various protocols; however, the most common treatment option is CHOP, which is composed of different chemotherapy drugs (cyclophosphamide, doxorubicin, vincristine, and prednisone), Some protocols may also include a chemotherapy agent called cytarabine, which some studies suggest may help with overall survival times. Depending on how aggressive the leukemia is, hospitalization and blood transfusions may be necessary. 

There are several different types of acute leukemias that each carry a different prognosis; however, the overall survival times unfortunately range from two weeks to four to six months, even with treatment. 

Chronic

Chronic leukemia tends to progress more slowly and has a more favorable outcome.

Dogs with chronic leukemia tend to feel well and do not have any clinical signs. Typically, the only abnormality is an elevated white blood cell count. Some dogs may have slightly enlarged lymph nodes; others may be slightly lethargic or have decreased appetites. 

Once the elevated white blood cells have been discovered, the same diagnostic tests explained above may be recommended. Given that this disease progress is slow-growing, treatment may not be initiated immediately. Monitoring with regular complete blood counts (CBC) may be recommended instead. Often, treatment is only started if the patient is clinically ill, the white blood cell counts are above 30,000-60,000, or lymph nodes are substantially enlarged and causing discomfort.

Treatment for this type of disease typically includes steroids and oral chemotherapy given at home. Most canine patients tolerate chemotherapy well with minimal side effects. Most side effects can be managed with medications that are often sent home at the beginning of therapy. General side effects include decreased appetite, vomiting, diarrhea, and a low white blood cell count. Regular monitoring with bloodwork is recommended to monitor for disease progression and to the dog is tolerating chemotherapy well. In rare cases, there is the potential for chronic leukemias to mutate into the acute form of leukemia.

Chronic lymphocytic leukemia has a much better response to treatment due to the slowly progressive nature of the disease. Often, an oral chemotherapy called chlorambucil is combined with prednisolone and is administered at home every other day to control the cancer.

Chronic lymphoid leukemia is very rare in cats and does not seem to be induced by FeLV infection. Cats with this condition often have a survival time of up to two years, depending on response to therapy. Diagnostics primarily include a complete blood count (CBC) and FeLV and FIV testing. Flow cytometry to assess molecular markers on the cells to characterize the type of leukemia may also be recommended. In some instances, a bone marrow aspirate or biopsy may be recommended. 

As with all cancers, early conversations with your primary care veterinarian and a follow-up consultation with a board-certified oncologist are always highly recommended.

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