Acute myeloid leukemia in dogs is a neoplastic disorder of dogs defined as elevated levels of circulating immature leucocytes (lymphoblasts).
In most dogs, it is recognized as a primary hematological variant of canine lymphoma.
This condition may occur as a primary disease or secondary to other causes (e.g. histiocytic sarcoma) and may involve all leucocytes or a particular subset.
Although the cause of primary leukemia in dogs is unknown, the pathogenesis appears to involve critical hematological components, particularly leukemia initiating cells which develop as a result of age-related and breed-predisposed genetic mutations in hematopoietic stem cell lines that overwhelm the pituitary production of leukemia inhibitory factor. These leukemia initiating cells consequently invoke changes in matrix metalloproteinases and vascular endothelial growth factors which cause most of the hemodynamic features of the disease.
The forms of leukemia reported in dogs include:
- Basophilic leukemia
- Dendritic cell leukemia
- Eosinophilic leukemia - to be differentiated from hypereosinophilic syndrome
- Erythroid leukemia - characterized by pancytopenia
- Intravascular lymphoma (NK cell origin) with overt leukemia
- Lymphocytic leukemia
- - B-cell lymphocytic leukemia-lymphoma complex
- - T-cell lymphocytic leukemia - anemia, neutropenia and thrombocytopenia - predispositon in the Golden Retriever
- - characterized by megakaryocytosis, with neoplastic megakaryoblasts can be identified in spleen, liver, mesenteric lymph nodes and pulmonary vasculature
- Metastatic carcinocythaemia (carcinoma cell leukaemia)
- Monocytic leukemia - leucocytosis, monocytosis - predisposition in the German Shepherd
- Myeloblastic leukemia - predisposition in the Golden Retriever
Blood tests often reveal varying degrees of non-regenerative anemia and leucocytosis, but unusual cases may present with subset disorders such as monocytosis, lymphopenia, neutropenia or thrombocytopenia. Other symptoms include lymphadenopathy and splenomegaly.
Rarely, skin involvement may be the first manifestation of acute leukemia, in which the bone marrow biopsy shows a precursor lesion (myeloproliferative or myelodysplastic syndrome) or normal findings. Rare forms of secondary disease include granulocytic sarcoma.
A presumptive diagnosis can be established based on clinical findings, hematological analysis of blood samples and thoracic and abdominal radiographs (to exclude tumors) and biopsies of bone marrow tissue.
Definitive diagnosis requires histopathological examination of bone marrow samples, immunohistochemical analysis (using CD61 and von Willebrand factor), PCR testing for detection of the NK cell and bcr-abl fusion gene mutations.
A differential diagnosis would include other causes of leucocytosis including myelodysplasia syndrome and myeloproliferative neoplasms (e.g. polycythemia vera, multiple myeloma, hemangiosarcoma and lymphoma)
Whole blood transfusion may be required in severely anemia patients and chemotherapy is recommended in most cases.
Numerous regimens of drugs is usually recommended as resistance to many combinations have been reported. Various chemotherapy combinations include:
- prednisolone and imatinib
- prednisolone and hydroxyurea
- prednisolone, daunorubicin, vincristine and cytosine arabinoside
- prednisolone and chlorambucil
The prognosis in many cases in dogs is guarded, particularly in younger dogs since many are detected at advanced stages.
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