Chronic granulocytic leukemia in a dog

A 4-year-old spayed dog had a recent history of increased WBC count and surgery for pyometra. Two weeks after surgery, WBC count was 57,640 cells/microliter; neutrophilia and immature myelocytic cells were detected. Histologic examination of liver and lymph node biopsy specimens revealed active granulopoiesis. Immature granulocytes that stained with chloroacetate esterase were evident. Bone marrow was excessively cellular and contained numerous granulocytes and blast cells. A diagnosis of chronic granulocytic leukemia was made on the basis of test results. Treatment with hydroxyurea returned the WBC count to reference range within 2 months. Mean survival time for dogs with chronic granulocytic leukemia is approximately 1 year; the dog of this report has remained healthy for more than 2 years. Chronic granulocytic leukemia is a rare neoplastic disease that must be differentiated from leukemoid inflammatory reactions. Although commonly described as a diagnosis determined by exclusion, diagnosis of chronic granulocytic leukemia should be made on the basis of specific criteria.