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J Vet Diagn Invest. 2017 Jul;29(4):529-535. doi: 10.1177/1040638717707724. Epub 2017 May 3.

Acute leukemia in six horses (1990-2012).

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Departments of Clinical Sciences, Cornell University, Ithaca, NY (Barrell, Felippe, Divers), College of Veterinary Medicine, Cornell University, Ithaca, NY.
Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, NY (Asakawa, Stokol), College of Veterinary Medicine, Cornell University, Ithaca, NY.


Acute leukemia is rare in horses. Herein we describe historical, clinicopathologic, and postmortem findings in 6 horses with acute leukemia. Medical records of horses with >20% bone marrow blasts and cytochemical or immunophenotyping results were reviewed. Affected horses were 2-8 y of age and of different breeds and sex. Horses were presented acutely with nonspecific signs (e.g., fever, lethargy). Characteristic hemogram findings were bi- or pancytopenia with low blast numbers. Histologic examination revealed extramedullary infiltrates, especially in lymph nodes, spleen, kidney, liver, and lungs. Leukemias were classified as B-cell ( n = 3) and acute myeloid leukemia (AML) ( n = 3). Tumors in 4 cases expressed multiple lineage markers, which complicated classification. Acute leukemia should be suspected in horses with moderate-to-severe bi- or pancytopenia. Blood smears should be reviewed for neoplastic cells, and bone marrow examination is required for diagnosis. Leukemia classification is best achieved using combined morphologic, cytochemical, and immunophenotyping results.


Acute lymphoblastic or myeloid leukemia; equine

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