Myeloproliferative disorders. Classification and diagnostic features with special emphasis on chronic myelogenous leukemia and agnogenic myeloid metaplasia. Leukocytosis, mild anemia, thrombocytosis, and panhyperplasia in the marrow characterize the early stages of most of the CMPD, whereas extramedullary hematopoiesis (such as in the spleen or liver), peripheral cytopenias (anemia, leukopenia, or thrombocytopenia), and myelofibrosis, with or without osteosclerosis, reflect the changes seen in the later stages. Transitions among the different CMPD and termination in acute leukemia or marrow failure also are common. CML often is characterized by leukocytosis and the presence of the entire spectrum of granulocytes (mature and immature) in the blood and marrow, reduced LAP, hypercellularity with prominent granulocytic hyperplasia in the marrow, Ph chromosome, and bcr-abl gene rearrangement. Typical features of AMM include leukoerythroblastosis, teardrop poikilocytosis, anemia, increased or normal LAP, prominent megakaryocytic hyperplasia in the marrow, dyshematopoiesis, and hyperplastic or fibrotic/sclerotic marrow. 