Chronic Lymphocytic leukemia (CLL) is a condition in which mature (i.e., "normal looking") lymphocytes (a type of white blood cell) accumulate in the body (including in the bone marrow and spleen).  This results in elevated circulating lymphocyte counts on CBC blood tests. CLL typically occurs in middle age to older dogs and is often found "accidentally" when blood work is being performed for other reasons.  CLL usually progresses slowly and patients can typically be medically managed and live well for years.
 

What causes CLL?

The causes of CLL in dogs, cats or people are unknown. We do know that something happens to the DNA of the cells that make these blood cells.
 

What are the common signs of CLL?

• Most patients with CLL are asymptomatic
• If symptoms are present they are typically vague signs of lethargy (decreased energy), decreased activity, or decreased appetite
• Mild lymphadenopathy (lymph node enlargement) and splenomegaly (enlargement of the spleen) can also be seen
• Some patients will have a mild anemia (low red blood cell count) and/or thrombocytopenia (low platelet count) along with varying degrees of a lymphocytosis (too many lymphocytes in the blood). 

How is CLL diagnosed?

• CBC (with pathology review)/chemistry panel/urinalysis
• 3 view chest radiographs
• Abdominal ultrasound
• Bone marrow aspirate/evaluation
• Immunophenotyping via flow cytometry of the blood to determine lymphocyte subset (T-cell vs B-cell)

The diagnosis is typically confirmed with a bone marrow aspiration.

How is CLL treated?

• Treatment is usually in the form of oral chemotherapy with prednisone and chlorambucil (Leukeran)
• Periodic monitoring of blood cell counts and physical examinations are required
• In some cases dogs may require stronger treatment such as intravenous chemotherapy either to help induce a remission or in cases where the patient is no longer responding to the oral therapy. 

What is the prognosis for dogs with CLL?

Even though complete remissions are usually not achieved, prognosis with therapy is good with median survival times ranging from 1-3 years. These animals typically have a great quality of life.

What is on the horizon for CLL?

Targeted therapies are increasingly being used to treat various malignancies and some of these oral drugs are being investigated as a treatment for this disease. As bone marrow transplantation becomes more available, it may become an important treatment for this disease.

Contributed by:  The Veterinary Cancer Center