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Myeloid cells arise from a common stem cell whose development is regulated by stimulatory and inhibitory growth factors. Pluripotential hematopoietic stem cells are most influenced by IL-3, GM-CSF, and stem cell factor while committed progenitor cells are regulated by variable concentrations of GM-CSF, G-CSF, M-CSF, IL-5, Epo, and Tpo. As a result of their common origin, a key point to remember about myeloproliferative disorders is the involvement of multiple cell lines in dysplastic and neoplastic conditions. Dysplastic changes may signal early neoplastic changes with cases progressing to acute leukemia. Myelodysplastic syndrome (MDS) is associated with anemia or multiple cytopenias, normal to hypercellular bone marrow, ineffective hematopoiesis, and less than 30% blast cells of all nucleated cells in the bone marrow. Chronic myeloid leukemias also have less than 30% blast cells of all nucleated cells in the bone marrow and are distinguished from MDS by elevated cell counts of one or more cell lines with mature forms predominating. Acute myeloid leukemias, often the end result of all myeloproliferative disorders, are recognized by equal or greater 30% blast cells of all nucleated cells in the bone marrow. Additional diagnostic information from cytochemical stains, immunohistochemical staining, and cytogenetic analysis can influence the final diagnosis when morphology alone is equivocal. In conclusion, prognosis and response to treatment are best determined by application of a uniform set of standards in evaluating hematolymphatic neoplasia. Critical to diagnosis are complete blood and bone marrow evaluations including observation for dysplastic changes and blast cell quantitation. In addition, evidence for tissue infiltration identified through cytologic or histologic evaluations of lymph node, spleen, or liver is recommended.

In the differential diagnosis of neoplastic diseases of blood cells or their precursors, cytological examination of bone marrow is a valuable diagnostic tool. Depending on the expected cell type, an aspiration followed by clinical-cytological examination, or a biopsy followed by histopathological examination is indicated. In all unclear cases of cytopenia, if blood parasites or a lymphatic leukemia without tumors are suspected or in myeloproliferative diseases, bone marrow cytology can provide the diagnosis. If the aspiration of bone marrow is not possible in spite of correct technique (punctiosicca), myelofibrosis must be suspected. The diagnosis is confirmed by bone marrow biopsy. In the most common form of leukemia in dogs, the lymphosarcomatosis, a bone marrow biopsy can be helpful in assessment of the prognosis.