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

Leukemia cutis as a prominent clinical sign in a dog with acute myeloid leukemia

An eight-year-old male neutered crossbreed dog presented with erosive and ulcerative cutaneous lesions in the inguinal regions, the medial aspect of both thighs, and the stifles. Hematologic assessment revealed nonregenerative anemia, thrombocytopenia, and high numbers of neoplastic mononuclear cells with a variable degree of maturation. The mononuclear neoplastic cells, with nuclei measuring 10-20 microns in diameter, accounted for 57% of the nucleated blood cells. In addition, the blood contained increased numbers of mature neutrophils and monocytes with atypical morphology. Cytologic examination of the right popliteal lymph node found high numbers of large mononuclear cells with similar morphology to those in the peripheral blood. Flow cytometry of peripheral blood revealed expression by the mononuclear neoplastic cells of the pan-leukocyte marker CD45 and myeloid markers CD14, MAC387, and myeloperoxidase (MPO). These results confirmed a diagnosis of acute myeloid leukemia (AML). Computed tomography found moderate nodular hepatosplenomegaly and multifocal bi-cavitary lymphadenopathy. Histopathologic examination of biopsies from the cutaneous lesions identified infiltration of the dermis by intermediate to large neoplastic round cells. Further treatment was declined, and the owners elected euthanasia. Postmortem examination confirmed AML involvement in the bone marrow, peripheral and intracavitary lymph nodes, heart, liver, kidney, and skin. Neoplastic cells in the bone marrow and skin showed positive immunolabeling for ionized calcium-binding adaptor protein 1 and MPO. To the best of our knowledge, this is the first report of ulcerative cutaneous lesions observed among the presenting clinical signs in a dog with AML and secondary leukemia cutis.

Neurological manifestations in dogs with acute leukemia

Canine acute leukemia is a rare hematopoietic neoplasm. Neurological abnormalities have been frequently reported in dogs with acute leukemia (AL). However, the description of the presentation and findings are limited. This study aimed to describe the clinical findings in dogs with acute leukemia presenting with neurological signs as their primary complaint. The database of a private referral hospital was searched for cases that presented to the neurological department with neurological deficits and were subsequently diagnosed with acute leukemia. Six cases were included; all had neurological clinical signs and an abnormal neurological examination. All cases had a focal neuroanatomical localisation on neurological examination (brain n = 4; spinal = 2). Out of the four dogs with a complete magnetic resonance imaging (MRI) study, there was an ill-defined infiltrative pattern with abnormal signal intensity in the central nervous system (CNS) in three dogs and the loss of grey and white matter differentiation in the brain (n = 2) and/or spinal cord (n = 2). Other MRI findings included abnormal meningeal enhancement (n = 3), changes affecting spinal nerves and epaxial muscles (n = 2), and lymphadenopathy in the field of view (n = 2). The bone marrow assessment on MRI showed evidence of signal change (n = 3), characterized by a loss of normal fat opacity and an abnormal degree of contrast enhancement. The cerebrospinal fluid (CSF) analysis of the four dogs showed an increased protein level with non-specific pleocytosis and without evidence of malignant cells. Treatment with cytotoxic medication was implemented in two dogs. The dogs diagnosed with acute leukemia had focal neuroanatomical localisation, an infiltrative CNS pattern, and bone marrow remodulation on MRI with an increase in CSF protein and negative cytology analysis.

Treatment of myeloid neoplasia with doxorubicin and cytarabine in 11 dogs

Myelodysplastic syndrome (MDS) and acute myeloid leukaemia (AML) are primary myeloid neoplasms in dogs generally considered to have a poor outcome. In this study, we assessed toxicity, efficacy and outcome of concurrent administration of doxorubicin and cytarabine in 11 dogs with myeloid neoplasia. Bone marrow specimens were reviewed by three pathologists and classified as either MDS (n = 2), high grade MDS/early AML (MDS/AML; n = 4) or AML (n = 5). The median number of treatment cycles was 5 (range 1-9) and resolution of cytopenia was reported in 7 of 11 dogs including 2 dogs with MDS, 2 dogs with MDS/AML, and 3 dogs with AML. The median duration of remission in the seven responders was 344 days (range 109-1428) and the median overall survival for all dogs was 369 days. Adverse events consisted of predominantly low-grade gastrointestinal illness and myelosuppression. Three dogs developed grade V toxicity manifesting with heart failure (n = 2) at 369 and 1170 days after diagnosis and acute gastrointestinal side effects (n =1). Despite a limited sample size, these results suggest that a doxorubicin and cytarabine protocol may be considered as a therapeutic option in dogs with myeloid neoplasia. Protocol safety, in particular regarding myocardial toxicity, and efficacy should be further investigated.

Pathological and immunohistochemical aspects of acute megakaryoblastic leukaemia in a cat - Short communication

An adult, mixed-breed, feline leukaemia virus (FeLV-) positive female cat was presented with mucosal jaundice and a history of anorexia and constipation for three days. Physical examination revealed splenomegaly, cachexia, and dehydration. Humane euthanasia was conducted, followed by postmortem examination. Grossly, the cat was icteric, and presented hepatomegaly with multifocal white spots and splenomegaly. Histologically, the bone marrow was nearly completely replaced by a proliferation of megakaryocytes and megakaryoblasts, and there was a proliferation of fibrous connective tissue. Similar neoplastic proliferation was observed infiltrating the liver, lymph nodes, spleen, kidney, skeletal muscle, and lungs. Immunohistochemistry was performed for von Willebrand Factor (VWF), CD79α, CD3, feline immunodeficiency virus, FeLV, and CD61. Marked cytoplasmic labelling was observed in the neoplastic cells for FeLV, VWF and CD61, corroborating the diagnosis of acute megakaryoblastic leukaemia.

A review of current knowledge of myeloproliferative disorders in the horse

Myeloid disorders are conditions being characterized by abnormal proliferation and development of myeloid lineage including granulocytes (neutrophils, eosinophils and basophils), monocytes, erythroids, and megakaryocytes precursor cells. Myeloid leukemia, based on clinical presentation and proliferative rate of neoplastic cells, is divided into acute (AML) and myeloproliferative neoplasms (MPN). The most commonly myeloid leukemia reported in horses are AML-M4 (myelomonocytic) and AML-M5 (monocytic). Isolated cases of AML-M6B (acute erythroid leukemia), and chronic granulocytic leukemia have also been reported. Additionally, bone marrow disorders with dysplastic alterations and ineffective hematopoiesis affecting single or multiple cell lineages or myelodysplastic diseases (MDS), have also been reported in horses. MDSs have increased myeloblasts numbers in blood or bone marrow, although less than 20%, which is the minimum level required for diagnosis of AML. This review performed a detailed description of the current state of knowlegde of the myeloproliferative disorders in horses following the criteria established by the World Health Organization.

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.

Thrombocytosis in 715 Dogs (2011-2015)

BACKGROUND

Thrombocytosis is a hematologic abnormality in dogs that has been associated with various neoplastic, metabolic, and inflammatory conditions.

OBJECTIVE

To classify thrombocytosis in dogs based on severity and evaluate whether there are associations between severity and underlying disease processes.

ANIMALS

Seven hundred and fifteen dogs with thrombocytosis and 1,430 dogs with normal numbers of platelets.

METHODS

Retrospective study. Medical records of dogs with increased (>500 × 10³ /μL; thrombocytosis group) and normal (300-500 × 10³ /μL; control group) platelet counts between 2011 and 2015 were reviewed. Dogs were characterized by severity of platelet increase and diagnosis. Diagnostic categories included neoplasia, endocrine disease, inflammatory disease, or miscellaneous.

RESULTS

A total of 1,254 complete blood counts with thrombocytosis from 715 dogs were included in the study. Median platelet count in this population was 582 × 10³ /μL (500-1,810 × 10³ /μL). No correlation between severity of thrombocytosis and diagnosis was identified. Causes of secondary thrombocytosis included neoplasia (55.7%), endocrine disease (12.0%), and inflammatory disease (46.6%). Immune-mediated disease was common (22.2%), associated with frequent glucocorticoid administration, and had a significantly higher median platelet count (636 × 10³ /μL [500-1,262 × 10³ /μL] versus 565 × 10³ /μL [500-1,810 × 10³ /μL]) when compared to the other inflammatory processes (P < 0.001). The diagnoses in the thrombocytosis dogs differed significantly from the control population (P < 0.001).

CONCLUSIONS AND CLINICAL IMPORTANCE

Thrombocytosis is commonly associated with carcinoma and immune-mediated disease in dogs.

Marked hyperphosphatasemia associated with an acute leukemia in a Great Dane

This is the report of a 5-year-old male neutered Great Dane with an extreme leukocytosis (544.9 × 10(9) cells/L; RI 5.2-13.9 × 10(9) cells/L) characterized by highly atypical round cells. Cellular morphologic features such as cytoplasmic membrane blebs, a high nuclear-to-cytoplasmic ratio, and nuclear indentations and irregularities and large nucleoli, as well as immunocytochemistry for CD3 and CD79, myeloperoxidase cytochemistry, and clonality testing were not conclusive for myeloid or lymphoid origin. Marked alkaline hyperphosphatasemia was present at the first visit (2783.0 U/L; RI 6-80.0 U/L), followed by a 5-fold increase (14,000 U/L) a week later, identified as being mostly contributed by the bone-ALP isoform (11,062 U/L; RI 0-30 U/L). In addition, the atypical leukocytes were strongly positive for cytoplasmic ALP activity. In vitro lysis of a heparin blood sample resulted in a 1.7-fold increase of ALP activity, supporting the origin of the hyperphosphatasemia at least in part from the leukemic cell population. To the authors' knowledge, this is a unique case of alkaline hyperphosphatasemia, due at least to a leukemic cell population producing a bone-ALP isoform, regardless of the exact nature of the leukemia.

Prognostic factors in canine acute leukaemias: a retrospective study

Canine acute leukaemias (ALs) have a poor prognosis, with reported survival times (ST) of only a few weeks or months. Also, clinical studies assessing prognostic factors are lacking. This study aims to retrospectively assess variables that predict ST in dogs with AL, and to identify correlations between outcome and therapeutic protocols. Diagnosis and sub-classification into AL subtypes was made based on haematological findings, morphological assessment and flow cytometric immunophenotyping. Clinical-pathological features of AL subtypes at presentation concurred with those described in the literature. A normal neutrophil count at presentation significantly prolonged ST (P = 0.027). Additionally, there was a trend for anaemic dogs to have shorter survival compared with those without anaemia, and the incorporation of cytosine in the chemotherapy protocol produced a moderate but not significant increase in median ST for dogs with AL. Further prospective studies with standardized treatments are needed to confirm and improve our results.