Acute megakaryoblastic leukemia in dogs: a report of three cases and review of the literature.

Three dogs of different breeds, ages, and genders were presented with pale mucous membranes, depression, anorexia, and splenomegaly. Observed were severe normocytic, nor-mochromic, nonregenerative anemia, thrombocytopenia, and leukopenia. Blood smears contained large, atypical cells with blue vacuolated cytoplasm, cytoplasmic blebs, round to oval central nuclei, and elevated numbers of cytoplasmic fragment resembling macroplatelets. Bi- and multinucleated atypical cells were found mainly in spleen, lymph nodes, and bone marrow. A final diagnosis of acute megakaryoblastic leukemia (AMegL) was made based on morphology and positivity to the megakaryocyte-derived cell-specific markers von Willebrand factor and CD61. In case nos. 1 and 2, no treatment was initiated, and the dogs died on days 4 and 3, respectively. Case no. 3 received supportive therapy with prednisone, and after a brief improvement the dog died spontaneously 35 days after initial presentation. Only 11 cases of AMegL have been reported in dogs, and the specific diagnostic criteria have not been well established. The presence of vacuolization, cytoplasmic blebs, central round nuclei, cytoplasmic fragments, and multinucleated cells in these three cases were considered useful to differentiate AMegL from other hematopoietic neoplasms.