Lymphoid leukemias are rare malignant cancers that originate from the white blood cells in the bone marrow.

In chronic lymphoid leukemia, the prominent cell is usually a more differentiated (mature) cell. They are less aggressive and the disease has a long duration of development with slower dividing or replication times.

Treatment is initiated with an alkylating agent (chlorambucil) with or without prednisone.

Chronic lymphoid leukemia carries a good prognosis with median survival times of a year to a year and a half without treatment and survival times of over two years with treatment.

What is Canine Chronic Lymphoid Leukemia?

• Lymphoid leukemias are rare malignant cancers that originate from the white blood cells in the bone marrow.
• Instead of maturing into normal cells, these precursor cells divide and replicate in an immature and non-functional form.
• These cells may be found circulating in the blood stream and/or in the bone marrow.
• Lymphoid leukemia can be classified by whether they appear in the blood stream or only appear in the bone marrow.   They can be further classified as acute or chronic based on the biological behavior and timeframe of the disease.
• In chronic lymphoid leukemia, the prominent cell is usually a more differentiated (mature) cell. They are less aggressive and the disease has a long duration of development with slower dividing or replication times.
• Some of the known causes of leukemia include radiation exposure and some viruses, but they are known to spontaneously develop too.

Clinical Signs

• There is no known breed or sex predilection for chronic lymphoid leukemia.  
• The age of disease onset varies widely with ranges from one to twelve years of age and with medians around 5.5 years old.
• The clinical signs of Lymphoid Leukemias are often non-specific and vary depending on the type of leukemia and the duration of the disease.
• The common signs of leukemia that owners often see at home are variable but may include:
  • lethargy
  • anorexia
  • weight loss
  • shifting leg lameness
  • fever
  • vomiting
  • diarrhea
  • increased drinking and urination.
• Common signs of leukemia that your veterinarian detect include:
  • increased liver or spleen size (hepatomegaly or splenomegaly)
  • mild increases in the lymph node size (mild lymphadenopathy)
  • pale mucous membranes
  • fever
  • bruises along the gums (petechiae)
  • eye disorders (ocular lesions)
  • lameness
  • neurological signs
  • these patients are often not clinically and critically ill.

Diagnosis

• The diagnosis of chronic lymphoid leukemia is done by clinical signs and laboratory tests. The most common tests used to confirm leukemia are:
  • complete blood count (CBC) – This is to determine the number and percentages of each type of cell in the blood. In leukemia abnormal cells are often seen in the circulation and increased numbers of lymphocytes are often seen. Additionally, the leukemia can cause decreases in other cell lines like red blood cells (anemia) and platelets (thrombocytopenia).
  • routine blood work on pets with leukemia will often show decreases in red blood cells or platelets (cytopenias or pancytopenias). They often show a marked increase in the circulating lymphocytes, often over 20,000 and increases in the circulating proteins and antibodies (monoclonal gamopathies). bone marrow aspirate – This will determine if abnormal numbers of immature lymphocytes are present in the bone marrow. In cases of sub-leukemic leukemia, the abnormal cells may only be present in the bone marrow and not seen in circulation on the CBC.
  • fine needle aspirate of spleen or liver if enlarged – If the organ enlargement is caused by infiltration by the lymphoid cells, then this may be found on cytology of the organs aspirated.
  • serology to rule out other causes of an increased white blood cell count – Often blood work is performed to look for other causes of an increased white blood cell count (infectious diseases). These tests are used to look for more easily treatable diseases that have similar clinical signs and laboratory results. Other causes with similar clinical signs and blood work values include infectious diseases (rickettsial diseases and hemobartonella) and other types of cancer (lymphosarcoma, lymphosarcoma cell leukemia, histiocytosis, mast cell leukemia).
  • Cytochemical staining – These are special stains performed on the blood or bone marrow to determine the origin and type of leukemic cells. This may be used to verify the disease or may change the prognosis or treatment.

Treatment

• Treatment is initiated with an alkylating agent (chlorambucil) with or without prednisone.
• There is usually a delay in response after treatment of up to a month. This delay is due to the slow growing nature of the cancer cells.
• Treatment failures most often occur due to failure to induce remission, due to organ failure from leukemia infiltration, or due to fatal sepsis or bleeding from the cytopenias.

Complications

• Complications associated with chemotherapy
  • bone marrow suppression with increased risk of anemia, infection, and bleeding,
  • nausea
  • liver toxicity

Prognosis

• Chronic lymphoid leukemia carries a good prognosis with median survival times of a year to a year and a half without treatment and survival times of over two years with treatment.