BCR-ABL translocation in a dog with chronic monocytic leukemia

A 9-year-old female spayed mixed breed dog was evaluated at the University of Florida Small Animal Hospital for marked leukocytosis with no associated clinical signs. CBC abnormalities included marked leukocytosis (106,000/μL), marked monocytosis (78,000/μL), and the presence of 13% blast cells (13,832/μL), supporting a diagnosis of leukemia. Cytopenias and dysplastic changes in other cell lines were not present. Microscopic examination of bone marrow showed hypercellular uniparticles with a marginal increase in frequency of unclassified blast cells (2%), but was otherwise unremarkable. Flow cytometric immunophenotyping of blood cells determined that leukemic cells were CD45(+) , CD14(+) , and CD34(-) , and based on side scatter and CD45 reactivity the marrow contained 19% monoblasts. By immunocytochemical staining, the leukemic cells in the bone marrow were CD11b(+) , CD11c(+) , CD11d(+) , MHC-II(+) , MPO(+) , and CD34(-) . Fluorescence in situ hybridization (FISH) analysis of peripheral blood leukocytes documented a chromosomal translocation producing a BCR-ABL gene hybrid, similar to the "Philadelphia" chromosome abnormality recognized in human chronic myelogenous leukemia, as well as a phosphatase and tensin homolog (PTEN) gene deletion. Hydroxyurea therapy was attempted, but was ineffective; the dog died 7 months after initial presentation. Clinical and laboratory findings and the protracted course supported a diagnosis of chronic monocytic leukemia (CMoL) and, to our knowledge, this is the first case of CMoL with a BCR-ABL chromosomal abnormalitiy described in dogs. This may have clinical implications for treatment of dogs with chronic leukemias associated with particular genetic mutations. However, more case studies are needed to further characterize this disease.     

Identification of acute myeloid leukemia in dogs using flow cytometry with myeloperoxidase, MAC387, and a canine neutrophil-specific antibody

BACKGROUND: Flow cytometry may be used to determine immunophenotype or lineage of leukemic cells, but few antibodies are available that are specific for cells of monocytic and granulocytic lineage. OBJECTIVE: The purpose of this study was to evaluate the flow cytometric staining patterns of 3 commercial monoclonal antibodies for monocytes and granulocytes in clinically healthy dogs and in dogs with acute myeloid leukemia (AML). METHODS: Mouse antihuman macrophage antibody (MAC387), mouse anti-human myeloperoxidase (MPO), and a canine neutrophil-specific antibody (NSA) were evaluated using flow cytometry on blood from 6 clinically healthy control dogs, and on blood (n = 7) and/or bone marrow (n = 2) from 8 dogs with AML. A diagnosis of acute leukemia was confirmed by >30% blasts in bone marrow or >30% blasts in peripheral blood, together with bi- or pancytopenia, circulating CD34-positive blast cells, and clinical signs of disease. Leukemic samples also were evaluated using a wide panel of monoclonal antibodies. RESULTS: MAC387 stained neutrophils and monocytes from control dogs, although the staining profiles for the 2 cell types differed. MPO and NSA resulted in strong positive staining of neutrophils; MPO also stained monocytes weakly. Lymphocytes did not stain with any of the antibodies. One case was classified as AML of granulocytic lineage (AML-M1), 6 cases were classified as acute monocytic leukemia (AML-M5), and 1 case was classified as acute myelomonocytic leukemia (AML-M4). Neoplastic myeloblasts in the dog with granulocytic AML were positive for MPO, NSA, MAC387, and CD4. All monoblasts from the dogs with AML-M5 were positive for CD14, 5 of 6 were positive for MAC387, and 2 were positive for MPO. NSA staining was negative in the 2 dogs with AML-M5 in which it was evaluated. In the dog with AML-M4 variable percentages of blast cells were positive for CD14, MPO, MAC387, CD4, and NSA. CONCLUSIONS: Antigens identified by antibodies to MAC387, MPO, and NSA were expressed not just by normal mature neutrophils and monocytes, but also by neoplastic myeloblasts and monoblasts. These 3 antibodies may be useful as part of a wider panel for immunophenotyping AML in dogs.     

CD34+, CD41+ acute megakaryoblastic leukemia in a dog

A clinically normal, 5-year-old intact female German Shepherd dog was presented to the local veterinarian to be spayed. Results of a preoperative CBC included mild nonregenerative anemia, severe thrombocytopenia, and 17% unclassified cells. On cytologic examination of aspirates from the dog's enlarged spleen and peripheral lymph nodes, a population of primitive round cells that occasionally resembled megakaryocytes was observed. A bone marrow aspirate specimen was markedly hypercellular with approximately 65% of marrow cells comprising a homogeneous population of immature hematopoietic cells similar to those found in the spleen, lymph nodes, and peripheral blood. Using immunocytochemical stains with canine-specific antibodies, all neoplastic cells strongly expressed cytoplasmic CD41 and 20-70% of the neoplastic cells expressed CD34 weakly to moderately. Rare (<0.5%) neoplastic cells weakly expressed vWF. The cells were negative for all other markers. Based on these results and the morphology of the neoplastic cells, a diagnosis of acute megakaryoblastic leukemia (AMegL) was made. In spite of treatment, results of a CBC performed 1 week later indicated progressive anemia and thrombocytopenia, and the dog was euthanized. To our knowledge, this report documents the first case of canine AMegL diagnosed with both anti-canine CD34 and CD41 antibodies.     

Molecular cloning and expression of bottlenose dolphin CD34

In terrestrial mammals, the surface molecule CD34 is used as a marker to identify hematopoietic progenitor cells. To clarify whether CD34 expression can be used to confirm the undifferentiated state of hematopoietic-like cells isolated from the bone marrow of bottlenose dolphin, Tursiops truncates, we determined in this study the sequence of dolphin CD34 cDNA and analyzed its mRNA expression. Dolphin CD34 cDNA can be expressed as two forms, one that encodes a full-length version and a variant, truncated version of the gene. Both forms were detected in bone marrow mononuclear cells and in various tissues using RT-PCR. The truncated form was not detected in peripheral blood mononuclear cells, and neither form was detected in polymorphonuclear leukocytes. This is the first report on CD34 in marine mammals and our results suggest that dolphin CD34 may be a useful marker to identify hematopoietic progenitor cells.     

Expression of CD34 mRNA and protein in cattle

CD34 is a transmembrane glycoprotein expressed by hematopoietic progenitors and endothelial cells. It is used widely in the clinic for purification of human hematopoietic stem cells transplants, and as an endothelial marker for several species. The aim of this study was to produce an anti-bovine CD34 antibody and to characterize the expression of CD34 mRNA and protein in cattle tissues. The bovine CD34 cDNA was cloned by RT-PCR, and the expression of bovine CD34 mRNA investigated by RT-PCR and in situ hybridization. Polyclonal antibodies were raised against CD34 polypeptide fragments expressed in Escherichia coli, and affinity purified. Alternative splicing of bovine CD34 mRNA was observed. Both splice variants were readily observed in endothelium, while the variant encoding a truncated cytoplasmic domain was mostly undetectable in bone marrow mononuclear cells. A polyclonal antibody against an extracellular fragment of the CD34 polypeptide was characterized using Western blots, cytocentrifuge preparates, and paraffin sections. CD34 immunoreactivity was enriched in lineage-depleted bone marrow cells. The antibody labelled most blood vessel endothelia in fetal and adult cattle, with highest intensity in capillaries. Newly forming capillaries in granulation tissue were also stained. Lymphatic vessels and the endothelium of liver sinusoids were negative.     

Anti-CD71 antibody immunohistochemistry in the diagnosis of acute myeloid leukemia,subtype acute erythroid leukemia with erythroid dominance (AML M6-Er), in a retrovirus-negative cat

CD71 is an immunohistochemical marker used in diagnosing acute myeloid leukemia (AML) M6-Er in humans; however, to our knowledge, it has not been reportedly used for immunohistochemistry in veterinary medicine. We evaluated the pathologic features of AML M6-Er in a retrovirus-negative cat and used CD71 to support the diagnosis. A 4-y-old spayed female Scottish Fold cat was presented with lethargy, anorexia, and fever. Whole-blood PCR assay results for pro feline leukemia virus/pro feline immunodeficiency virus and feline vector-borne diseases were negative. Early erythroid precursors were observed in the peripheral blood smear. Fine-needle aspiration of the enlarged spleen and splenic lymph node showed many early erythroid precursors. Bone marrow aspirate smears revealed erythroid hyperplasia with 68.4% erythroid lineage and 3.6% rubriblasts. Dysplastic cells infiltrated other organs. The patient was diagnosed with myelodysplastic syndrome, progressing to the early phase of AML M6-Er. The patient died on day 121 despite multidrug treatments. Postmortem examination revealed neoplastic erythroblasts infiltrating the bone marrow and other organs. Neoplastic cells were immunopositive for CD71 but immunonegative for CD3, CD20, granzyme B, von Willebrand factor, CD61, myeloperoxidase, and Iba-1. Although further studies are necessary for the application of CD71, our results supported the morphologic diagnosis of AML M6-Er.     

In vitro selective suppression of feline myeloid colony formation is attributable to molecularly cloned strain of feline leukemia virus with unique long terminal repeat

Molecularly cloned feline leukemia virus (FeLV)-clone 33 (C-33), derived from a cat with acute myelocytic leukemia (AML), was examined to assess its relation to the pathogenesis of AML and myelodysplastic syndrome (MDS). To evaluate in vitro pathogenicity of FeLV C-33, bone marrow colony-forming assay was performed on marrow cells infected with FeLV C-33 or an FeLV subgroup A strain (61E, a molecularly cloned strain with minimal pathogenicity). The myeloid colony-forming activity of feline bone marrow mononuclear cells infected with FeLV C-33 was significantly lower than that of cells infected with 61E. This suggests that FeLV C-33 has myeloid lineage-specific pathogenicity for cats, and that FeLV C-33 infection is useful as an experimental model for investigating pathogenesis of MDS and AML.     

Immunophenotype and functional properties of feline dendritic cells derived from blood and bone marrow

Dendritic cells (DCs) are a heterogeneous population of cells of fundamental importance in initiating innate as well as specific immune responses. The identity and function of DCs in the cat are unknown, although they are likely pivotal in the response to infection. In this study, feline DCs were derived by 3-10-day culture of adherent blood mononuclear cells (PBMCs) and bone marrow mononuclear cells (BMMCs) in the presence of IL 4 and GM-CSF. BMMC consistently yielded a greater number of DCs than PBMC, and there were fewer macrophages than DC from both compartments. DCs expressed a distinct constellation of surface molecules, which included CD1a, CD1b, and CD1c, CD11b, CD14, and 2-3-fold higher levels of MHC class I and II molecules than co-cultured macrophages or fresh blood monocytes. DCs displayed typical cytoplasmic processes, limited non-specific esterase activity, and acquired antigen by phagocytosis, pinocytosis, and binding to specific receptors. Cytokine-exposed cells induced proliferation of allogeneic lymphocytes. Thus, the cells derived by these culture conditions had markers and functions analogous to immature myeloid DCs. Availability of feline DCs will enable investigation of their role in infectious disease and their potential therapeutic application.     

Proposed criteria for classification of acute myeloid leukemia in dogs and cats

Blood and bone marrow smears from 49 dogs and cats, believed to have myeloproliferative disorders (MPD), were examined by a panel of 10 clinical pathologists to develop proposals for classification of acute myeloid leukemia (AML) in these species. French-American-British (FAB) group and National Cancer Institute (NCI) workshop definitions and criteria developed for classification of AML in humans were adapted. Major modifications entailed revision of definitions of blast cells as applied to the dog and cat, broadening the scope of leukemia classification, and making provisions for differentiating erythremic myelosis and undifferentiated MPD. A consensus cytomorphologic diagnosis was reached in 39 (79.6%) cases comprising 26 of AML, 10 of myelodysplastic syndrome (MDS), and 3 of acute lymphoblastic leukemia (ALL). Diagnostic concordance for these diseases varied from 60 to 81% (mean 73.3 +/- 7.1%) and interobserver agreement ranged from 51.3 to 84.6% (mean 73.1 +/- 9.3%). Various subtypes of AML identified included Ml, M2, M4, M5a, M5b, and M6. Acute undifferentiated leukemia (AUL) was recognized as a specific entity. M3 was not encountered, but this subclass was retained as a diagnostic possibility. The designations M6Er and MDS-Er were introduced where the suffix "Er" indicated preponderance of erythroid component. Chief hematologic abnormalities included circulating blast cells in 98% of the cases, with 36.7% cases having >30% blast cells, and thrombocytopenia and anemia in approximately 86 to 88% of the cases. Bone marrow examination revealed panmyeloid dysplastic changes, particularly variable numbers of megaloblastoid rubriblasts and rubricytes in all AML subtypes and increased numbers of eosinophils in MDS. Cytochemical patterns of neutrophilic markers were evident in most cases of Ml and M2, while monocytic markers were primarily seen in M5a and M5b cases. It is proposed that well-prepared, Romanowsky-stained blood and bone marrow smears should be examined to determine blast cell types and percentages for cytomorphologic diagnosis of AML. Carefully selected areas of stained films presenting adequate cellular details should be used to count a minimum of 200 cells. In cases with borderline diagnosis, at least 500 cells should be counted. The identity of blast cells should be ascertained using appropriate cytochemical markers of neutrophilic, monocytic, and megakaryocytic differentiation. A blast cell count of > 30% in blood and/or bone marrow indicates AML or AUL, while a count of < 30% blasts in bone marrow suggests MDS, chronic myeloid leukemias, or even a leukemoid reaction. Myeloblasts, monoblasts, and megakaryoblasts comprise the blast cell count. The FAB approach with additional criteria should be used to distinguish AUL and various subtypes of AML (Ml to M7 and M6Er) and to differentiate MDS, MDS-ER, chronic myeloid leukemias, and leukemoid reaction. Bone marrow core biopsy and electron microscopy may be required to confirm the specific diagnosis. Immunophenotyping with lineage specific antibodies is in its infancy in veterinary medicine. Development of this technique is encouraged to establish an undisputed identity of blast cells. Validity of the proposed criteria needs to be substantiated in large prospective and retrospective studies. Similarly, clinical relevance of cytomorphologic, cytochemical, and immunophenotypic characterizations of AML in dogs and cats remains to be determined.     

小鼠髓源未成熟树突状细胞的分离与培养

本试验旨在建立一种体外诱导培养小鼠未成熟树突状细胞(dendritic cell,DC)的方法。应用重组粒细胞-巨噬细胞集落刺激因子(rGM-CSF)在体外诱导小鼠骨髓前体细胞分化为未成熟树突状细胞,进行形态学观察、细胞表型分析、刺激T细胞增殖等方法,对小鼠髓源未成熟树突状细胞的体外诱导培养进行鉴定。试验结果显示,小鼠骨髓来源的DC在体外培养8 d后,特异性细胞表面标志CD11c的表达量达到81.09%,中度表达MHCⅡ,低表达CD40、CD80、CD86。本试验成功地建立了体外小鼠髓源DC扩增的方法。     

Acute myeloid leukemia with basophilic differentiation (AML,M-2B) in a cat

A 4-year-old, neutered male Domestic Shorthair cat with a history of depression, anorexia, and weight loss was diagnosed with acute myelogenous leukemia (AML). The cat tested positive by both the feline immunodeficiency virus antibody test and feline leukemia virus enzyme-linked immunosorbent assay test. Results of cytochemical stains on peripheral blood and bone marrow specimens indicated acute myeloid leukemia with unusual basophilic differentiation (AML, M-2B).     

Flow cytometric analysis of bone marrow leukocytes in neonatal dogs

Dogs represent both an important veterinary species and a convenient model for allogeneic hematopoietic stem cell transplantation. Even though anti-canine CD34 antibodies have recently become available, little is known about hematopoietic lineages in dogs, partially because CD34- cells have been ignored in all analyses performed so far. In this study, we have focused on the bone marrow mononuclear compartment to provide an additional piece of information on the phenotype of CD34+ progenitors and to identify the dominant CD34- population. We have shown that, in contrast to the adults, mature lymphocytes are scarce in neonatal dog bone marrow. Using cross-reactive antibodies against CD79alpha we have shown that the B lineage of hematopoiesis strongly prevails. CD34+ cells were shown to be positive for MHC class II and SWC3, a member of the signal regulatory protein family.     

Chronic eosinophilic leukemia in a cat: cytochemical and immunophenotypical features

A 3-year-old, male, domestic shorthaired cat was presented with a 3-day history of anorexia and depression. The cat was moderately dehydrated, had pale, slightly icteric, mucous membranes, oral ulcerations, and mild hepatosplenomegaly. A feline leukemia virus (FeLV) antigen test was positive. CBC results obtained at initial presentation included severe normocytic, normochromic, nonregenerative anemia, severe thrombocytopenia, and marked leukocytosis (>100,000/microL) with 77% eosinophils. After 15 days of treatment with prednisone and doxycycline, the cat had persistent severe nonregenerative anemia (HCT 3.4%), thrombocytopenia (28,000/microL), and extreme eosinophilia (total eosinophils, 123.1 x 10(3)/microL; segmented 103.0 x 10(3)/microL; immature 20.1 X 10(3)/microL). Cytologic examination of aspirates from bone marrow, liver, lymph nodes, and spleen revealed a predominance of mature and immature eosinophils, many with dysplastic changes. The M:E ratio was 96.4. On histopathologic examination, multiple organs were infiltrated by eosinophilic granulocytes. Neoplastic cells in blood and bone marrow stained positive for alkaline phosphatase and were negative for myeloperoxidase, chloroacetate esterase, and alpha-naphthyl acetate esterase. On flow cytometric analysis of peripheral blood, the neoplastic cells were positive for CD11b and CD14. These findings were consistent with chronic eosinophilic leukemia. To our knowledge, this is the first report of chronic eosinophilic leukemia in a cat associated with naturally acquired FeLV infection, in which flow cytometry was used to characterize the neoplastic cells.     

Isolation and characterization of pediatric canine bone marrow CD34+ cells

Historically, the dog has been a valuable model for bone marrow transplantation studies, with many of the advances achieved in the dog being directly transferable to human clinical bone marrow transplantation protocols. In addition, dogs are also a source of many well-characterized homologues of human genetic diseases, making them an ideal large animal model in which to evaluate gene therapy protocols. It is generally accepted that progenitor cells for many human hematopoietic cell lineages reside in the CD34+ fraction of cells from bone marrow, cord blood, or peripheral blood. In addition, CD34+ cells are the current targets for human gene therapy of diseases involving the hematopoietic system. In this study, we have isolated and characterized highly enriched populations of canine CD34+ cells isolated from dogs 1 week to 3 months of age. Bone marrow isolated from 2- to 3-week-old dogs contained up to 18% CD34+ cells and this high percentage dropped sharply with age. In in vitro 6-day liquid suspension cultures, CD34+ cells harvested from 3-week-old dogs expanded almost two times more than those from 3-month-old dogs and the cells from younger dogs were also more responsive to human Flt-3 ligand (Flt3L). In culture, the percent and number of CD34+ cells from both ages of dogs dropped sharply between 2 and 4 days, although the number of CD34+ cells at day 6 of culture was higher for cells harvested from the younger dogs. CD34+ cells harvested from both ages of dogs had similar enrichment and depletion values in CFU-GM methylcellulose assays. Canine CD34+/Rho123lo cells expressed c-kit mRNA while the CD34+/Rhohi cells did not. When transplanted to a sub-lethally irradiated recipient, CD34+ cells from 1- to 3-week-old dogs gave rise to both myeloid and lymphoid lineages in the periphery. This study demonstrates that canine CD34+ bone marrow cells have similar in vitro and in vivo characteristics as human CD34+ cells. In addition, ontogeny-related functional differences reported for human CD34+ cells appear to exist in the dog as well, suggesting pediatric CD34+ cells may be better targets for gene transfer than adult bone marrow. The demonstration of similarities between canine and human CD34+ cells enhances the dog as a large, preclinical model to evaluate strategies for improving bone marrow transplantation protocols, for gene therapy protocols that target CD34+ cells, and to study the engraftment potential of various cell populations that may contain hematopoietic progenitor cell activity.     

Clonality analysis of various hematopoietic disorders in cats naturally infected with feline leukemia virus

The clonality analysis of the bone marrow cells was carried out by detecting the integrated proviruses of feline leukemia virus (FeLV) to understand the pathogenesis of FeLV-associated hematopoietic disorders in cats. Bone marrow cells from 4 cases with acute myeloid leukemia (AML), 9 cases with myelodysplastic syndromes (MDS), 2 cases with pure red cell aplasia (PRCA) and 3 healthy carriers infected with FeLV were subjected to Southern blot analyses using an exogenous FeLV probe. Clonal hematopoiesis was found in all the cases with AML and in 6 of the 9 cases with MDS, but not in the cases with both PRCA and healthy carriers infected with FeLV. In the 2 cases with MDS, it was thought that the same clones of the hematopoietic cells might proliferate before and after the progression of the disease irrespective of the changes of the hematological diagnoses by cytological examination. This study indicates that MDS in cats is a disease manifestation as a result of clonal proliferation of hematopoietic cells and can be recognized as a pre-leukemic state of AML.     

Monoblastic leukemia (M5a) with chronic basophilic leukemia in a cat

A cat was presented with depression and anorexia. The complete blood cell count (CBC) revealed non-regenerative anemia (PCV, 8.5%), marked thrombocytopenia (2,400/µl), and leukocytosis (32,090/µl). In the peripheral blood, proliferation of blast cells (85%; 27,276/µl) and basophils (7.7%; 2,460/µl) was observed. Bone marrow aspirate showed hyperplasia with 8.8% blasts and 90.2% basophils of all nucleated cells. The blast cells were negative for myeloperoxidase staining and positive for alpha-naphthol butyrate esterase staining, indicating the agranular blasts are monoblasts. Thus, acute monoblastic leukemia (M5a) with chronic basophilic leukemia was diagnosed. Basophils accounted for more than 40% of the bone marrow, and we diagnosed secondary basophilic leukemia. Secondary basophilic leukemia should be included in the differential list when abnormal basophil increases are observed in feline bone marrow.     

两种方法所获鸭破骨细胞数量及活性比较

对直接从鸭骨髓腔机械分离的成熟破骨细胞（osteoclasts,OC）和由鸭骨髓来源单核细胞融合成的OC样多核巨细胞（multinucleatedgiantcells,MNGCs）进行培养,分别进行抗酒石酸酸性磷酸酶（tartrate-resistantacidphosphatase,TRAP）染色并计数,扫描电镜观察象牙片吸收陷窝,比较了2种方法获得0C的骨吸收功能。结果显示,2种方法均能分离培养出TRAP阳性且具有骨吸收功能的多核OC,但直接分离获得的成熟OC骨吸收功能更强。     

Detection of feline immunodeficiency virus infection in bone marrow of cats.

Natural or experimental feline immunodeficiency virus (FIV) infection in cats is often associated with hematologic abnormalities which are similar to those observed in human immunodeficiency virus (HIV) infected patients. To determine if cells in bone marrow are infected with FIV and whether severity of hematopoietic disorder is correlated with the level of viral infection, bone marrow tissues from ten experimentally and two naturally FIV infected cats were examined by in situ hybridization for presence of FIV RNA. Seven of the 12 FIV infected cats were also naturally or experimentally coinfected with feline leukemia virus (FeLV). FIV RNA was detected mainly in megakaryocytes and unidentified mononuclear cells in the bone marrow of cats that were sick and had marrow hypercellularity and immaturity. These included all cats in the acute phase of FIV infection and two of seven long term FIV infected cats. One long term FIV infected cat with lymphosarcoma was also positive for FIV RNA in bone marrow cells. The other four long term FIV infected cats were relatively healthy, with normal bone marrow morphology, and were negative for FIV infected cells. Bone marrow from three non-infected and two cats infected with FeLV alone were also negative for FIV RNA by in situ hybridization. We concluded that megakaryocytes and mononuclear cells were targets of the viral infection and that the presence of FIV RNA in cells of the bone marrow correlated with marrow hypercellularity and immaturity, and severity of illness.     

Myelodysplasia, hypophosphataemia, vitamin D and iron deficiency in an alpaca.

A pregnant 2-year-old alpaca was presented for evaluation of progressive weight loss, decreased appetite and lethargy that developed in winter. Haematologic and serum biochemical analyses revealed marked anaemia, leukopenia, severe hypophosphataemia and mild hypocalcaemia. Evaluation of bone marrow core biopsies and aspirates revealed an increased proportion of immature haematopoietic cells, without sufficient numbers of blast cells to be termed an acute myeloid leukaemia (AML). 1 The haematological and bone marrow findings were suggestive of myelodysplastic syndrome (MDS). The anaemia, leukopenia, lethargy and weight loss remained refractory to medical therapy and the alpaca was euthanased on humane grounds.     

Myeloperoxidase-positive acute megakaryoblastic leukemia in a dog

A 16-month-old female spayed Labrador Retriever was referred to the University of Edinburgh for exercise intolerance, inappetence, and severe anemia. A CBC showed severe nonregenerative anemia and moderate numbers of atypical cells with morphologic features most consistent with megakaryoblastic origin. Similar cells were identified in a bone marrow aspirate and accounted for 23% of all nucleated cells. Atypical promegakaryocytes and megakaryocytes were also noted. Myelodysplastic syndrome affecting the megakaryocytic lineage was suspected. Cytologic examination of a fine-needle aspirate of the spleen revealed rare megakaryoblasts similar to those in blood and bone marrow. At necropsy, the bone marrow consisted of atypical megakaryoblasts and megakaryocytes that were also infiltrating spleen, liver, lymph nodes, renal perihilar tissue, and visceral adipose tissue, consistent with acute megakaryoblastic leukemia. Immunohistochemical analysis of splenic sections confirmed megakaryoblastic origin (immunoreactive for CD61 and von Willebrand factor). Some leukemic cells were also immunoreactive for myeloperoxidase (MPO). This aberrant immunophenotype suggested both megakaryocytic and granulocytic/monocytic differentiation of the leukemic cells. To our knowledge, this is the first report of MPO-positive acute megakaryoblastic leukemia in a dog.