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Myeloid neoplasms include cancers associated with both rapid (acute myeloid leukemias) and gradual (myelodysplastic syndromes and myeloproliferative neoplasms) disease progression. Percentage of blast cells in marrow is used to separate acute (rapid) from chronic (gradual) and is the most consistently applied prognostic marker in veterinary medicine. However, since there is marked variation in tumor progression within groups, there is a need for more complex schemes to stratify animals into specific risk groups. In people with acute myeloid leukemia (AML), pretreatment karyotyping and molecular genetic analysis have greater utility as prognostic markers than morphologic and immunologic phenotypes. Karyotyping is not available as a prognostic marker for AML in dogs and cats, but progress in molecular genetics has created optimism about the eventual ability of veterinarians to discern conditions potentially responsive to medical intervention. In people with myelodysplastic syndromes (MDS), detailed prognostic scoring systems have been devised that use various combinations of blast cell percentage, hematocrit, platelet counts, unilineal versus multilineal cytopenias and dysplasia, karyotype, gender, age, immunophenotype, transfusion dependence, and colony-forming assays. Predictors of outcome for animals with MDS have been limited to blast cell percentage, anemia versus multilineal cytopenias, and morphologic phenotype. Prognostic markers for myeloproliferative neoplasms (eg, polycythemia vera, essential thrombocythemia) include clinical and hematological factors and in people also include cytogenetics and molecular genetics. Validation of prognostic markers for myeloid neoplasms in animals has been thwarted by the lack of a large case series that requires cooperation across institutions and veterinary specialties. Future progress requires overcoming these barriers.

The combination of flow cytometric scatterplot analysis and specific monoclonal antibodies was used to evaluate the lineage of cells from six dogs with proliferative disorders of bone marrow. Scatterplot analysis was used to identify mature and immature myeloid and erythroid cells. The immunophenotype of cells in the immature myeloid gate was determined by labeling cells with four monoclonal antibodies. These results were compared to results of cytologic and cytochemical evaluation. The immunophenotype of a dog with a diagnosis of myelogenous leukemia was a cluster of differentiation-18 (CD-18) positive, CD-14 negative, Thy-1 negative, and a major histocompatibility complex (MHC) class II negative. The immunophenotype of a dog with a diagnosis of myelomonocytic leukemia was CD-18 positive, CD-14 positive, Thy-1 positive, and MHC class II positive. Although this phenotype clearly differentiated myelomonocytic leukemia from myelogenous leukemia, it was similar to the immunophenotype of dogs with a diagnosis of malignant histiocytosis or hemophagocytic syndrome. The immunophenotype of two dogs with myelodysplastic syndrome was CD-18 positive and CD-14 negative. Results for Thy-1 and MHC class II were variable. As additional lineage-specific monoclonal antibodies become available, immunophenotyping should become a valuable tool for determination of the lineage of cells in canine myeloproliferative disorders.

A 4 1/2-year-old cat had myeloproliferative disease characterized by severe anemia. Peripheral blood had a profusion of relatively normal-appearing nucleated erythroid cells in all stages of development and a few primitive cells with nucleoli. The term "erythremic myelosis" best described the appearance of the peripheral blood. Two weeks later, the peripheral blood picture was that of regenerative anemia. During the next 2 months the cat made an apparent clinical recovery without treatment, but relapsed 3 months after the initial examination. One-fourth of the cells in circulation at the time of relapse contained nucleoli and appeared identical to those described in reticuloendotheliosis in cats. This transition suggested the progressive development of a greater degree of immaturity of erythroid precusors with time. The use of the term "reticuloendotheliosis" in conjunction with feline myeloproliferative disease was considered and determined inappropriate.