Myeloperoxidase-positive acute megakaryoblastic leukemia in a dog

Thrombocytosis and central nervous system involvement in a case of canine acute megakaryoblastic leukemia

This case report presents a 14-month-old female Poodle mix with acute megakaryoblastic leukemia based on a marked thrombocytosis, abnormal platelet morphology, circulating dwarf megakaryocytes, and blast cells in the blood. Bone marrow abnormalities included dysmegakaryopoiesis dygranulopoiesis, and an increased number of blast cells was observed in the blood. Extensive leukemic involvement was also found in the liver, spleen, lymph nodes, lungs, kidneys, and brain. The cytopathologic features of the abnormal circulating cells were highly suggestive of being megakaryocytic in origin, which was supported by negative myeloperoxidase staining and positive von Willebrand factor staining on immunocytochemistry (ICC). The neoplastic cells were also CD61 positive and had variable von Willebrand factor expression on ICC. Although there were only 25% blast cells in the bone marrow, which theoretically supported myelodysplastic syndrome, the hypothesis that this case represented acute myeloid leukemia of megakaryoblastic origin was confirmed by the continuous increase in circulating blast cell numbers during follow-up visits and the extensive leukemic involvement of parenchymal organs.

A retrospective review of acute myeloid leukaemia in 35 dogs diagnosed by a combination of morphologic findings, flow cytometric immunophenotyping and cytochemical staining results (2007-2015)

Acute myeloid leukaemia (AML) is an uncommon, rapidly progressive neoplasm in dogs. The aim of this retrospective study was to characterize the clinical presentation, haematologic findings, diagnostic imaging results, treatment and survival time of a contemporary cohort of dogs with AML. Diagnosis was based on >20% blasts in bone marrow or blood identified as myeloid based on morphologic findings, flow cytometric immunophenotyping and cytochemical staining. Medical records of 35 dogs diagnosed with AML from 2007 to 2015 were included. Most dogs presented with inappetence (66%) and lethargy (57%) and physical examination findings of peripheral lymphadenopathy (74%) and tachypnea (62%). Common haematologic findings were quantifiable circulating blasts (85%; median blast count 35 700/μL; range: 300-276 500/μL), anaemia (median haematocrit 34%; range: 11%-52%) and thrombocytopenia (median 57 000/μL; range: 9000-252 000/μL). Bicytopenia and pancytopenia were each found in 44% of dogs. Follow-up information was available for 34 dogs. The overall median survival time from diagnosis was 19 days (range: 1-121 days). Clinical progression in some dogs was not as rapid as previously reported. Haematologic responses to various chemotherapeutics were documented in 3 dogs, with associated survival times of 62, 103 and 121 days. Dogs treated with prednisone or a combination of chemotherapy and prednisone had improved survival compared to dogs that received symptomatic care only (P < .0001). Our results show canine AML has an overlapping clinical presentation with lymphoma. The prognosis for canine AML remains extremely guarded. Further studies are needed to optimize therapeutic regimens for dogs with AML.