Acute megakaryoblastic leukemia in a German Shepherd dog

Abstract

An 11-year-old spayed-female German Shepherd dog was presented to the Veterinary Medical Teaching Hospital at Kansas State University with a history of weight loss, anorexia, depression, and lethargy for 2-3 weeks. Radiographic examination revealed a mass in the spleen and several round radiodense foci in the liver. CBC results included normocytic normochromic anemia, marked thrombocytopenia, and low numbers of neoplastic cells that frequently had cytoplasmic projections or blebs. A bone marrow aspirate contained about 80% neoplastic megakaryoblasts with the same microscopic features as those observed in peripheral blood. Using flow cytometry, cells of large size were identified in peripheral blood that expressed CD41/61, CD45, CD61, and CD62P (P-selectin) and were negative for markers of T cells, B cells, monocyte/macrophages, and dendritic cells. Because of the poor prognosis, euthanasia and subsequently necropsy were performed. On histopathologic examination, neoplastic megakaryoblasts were identified in spleen, liver, mesenteric lymph node, and the pulmonary vasculature. Using immunohistochemistry, the neoplastic megakaryoblasts weakly expressed von Willebrand factor. Based on microscopic and immunophenotypic findings, a diagnosis of acute megakaryoblastic leukemia (AMegL) was made. To our knowledge, this is the first report of AMegL in a domestic animal in which immunophenotyping by flow cytometry and a panel of antibodies against CD41/61, CD61, and CD62P were used to support the diagnosis.

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

“…More than 80% of the neoplastic cells were CD61 positive, whether they were multinucleated or not, as previously reported in eight cases of AML‐M7 . The inconsistent vWF positivity in the present case has already been reported in six of the cases of canine AML‐M7 that tested for vWF . In the case described here, only the more differentiated neoplastic cells (multinucleated) were positive for vWF.…”

“…Acute megakaryoblastic leukemia is a rare neoplastic disease of dogs, with only 18 spontaneous cases reported in the literature . Here, we report a case of AML‐M7 that raises the issue of the blast percentage threshold to distinguish MDS from acute myeloid leukemia (AML).…”

“…Thrombocytosis during initial diagnoses is an uncommon feature of canine AML‐M7 (only two cases reported); however, in contrast, thrombocytopenia is fairly common (15 cases reported). This case emphasizes the fact that AML‐M7 should be listed as a differential in cases of canine thrombocytosis.…”

Use of CD9 and CD61 for the characterization of AML‐M7 by flow cytometry in a dog*

“…To our current knowledge, only 14 cases of spontaneous AML‐M7 have been previously described and only two publications describe the use of flow cytometry for definitive diagnosis of AML‐M7 19,25 in veterinary medicine. On the basis of this further report, the German Shepherd dog seems overrepresented 6 accounting for six cases in the literature including this case. In accordance with other previous works, clinical outcome and prognosis for both people and dogs affected by AML‐M7 are poor.…”

“…CD34 immunoreactivity is usually considered supportive of acute leukaemia. However, this is not definitive, as it is known that a percentage of neoplastic blastic cells may lack CD34 expression in both canine and human patients 6 . Cells morphologically consistent with ‘blast cells' with or without CD34 expression were then categorized as myeloid based upon further immunophenotyping results 7 .…”