Chronic Myeloid Neoplasms

The chronic myeloid neoplasms or MPNs are usually associated with high numbers of circulating neoplastic cells. There is a greater degree of differentiation/maturation of the affected cell line in the chronic neoplasms. Theoretically, any of the neoplasms listed in the acute category could appear in a chronic form (Table 3.3). For instance, the division between the two may blur since a blast crisis (release of neoplastic blast cells into the peripheral blood) can occur with chronic myeloid neoplasms, mimicking acute myeloid leukemia. Most of the chronic myeloid neoplasms are rare in domestic animals. The chronic form of erythrocyte neoplasia has been reported in dogs, cats, horses, and cattle. This neoplasm is termed primary erythrocytosis in veterinary medicine, but polycythemia (rubra) vera in human medicine because cell lines in addition to red cells may be affected in humans, suggesting a stem cell disease. However, in animals, the disease appears to involve only the erythroid line. Unlike the acute erythrocytic neoplasm (M6Er) which is associated with nonregenerative anemia, chronic erythroid neoplasia is manifested as erythrocytosis with normal appearing erythroid cells and orderly maturation. The hematocrit is elevated and clinical signs relate to increased blood viscosity. Sludging of blood flow and decreased tissue perfusion can result in central nervous system signs, lethargy and blindness. Erythropoietin concentrations are low to normal since the clonal expansion of erythroid precursors is independent of normal growth factor controls.