An overview of the classic myeloproliferative neoplasms (MPN, myeloproliferative diseases [MPD]; eg, polycythemia vera, essential thrombocythemia, primary myelofibrosis, chronic myeloid leukemia) will be presented here [1,2]. Detailed information on each of these disorders is presented separately.
CLASSIFICATION OF HEMATOLOGIC MALIGNANCIES
The hematopoietic pluripotent stem cell is capable of both self-renewal and a stepwise differentiation, after a stochastic determination, into either the lymphoid or myeloid lineage . Thus, during normal hematopoiesis, there exists a cellular hierarchy headed by a stable population of pluripotent stem cells, which generate lineage-specific progenitors differentiating into the various types of mature blood cells . Effective hematopoiesis is facilitated by the interactive functions of hematopoietic growth factors, various sets of receptors, and the bone marrow microenvironment.
An operational classification of hematologic malignancies separates lymphoid from myeloid processes (figure 1). Each of these is in turn classified as being acute or chronic, depending upon the proportion of morphologically and immunophenotypically immature precursors (blasts) in the bone marrow. Thus, the myeloid hematologic malignancies are divided into acute myeloid leukemia (bone marrow blasts of 20 percent or more) and the chronic myeloid disorders (bone marrow blasts less than 20 percent).
The chronic myeloid disorders — The chronic myeloid disorders encompass several clinicopathologic entities. Conceptually, they can be organized into those which either display (the myelodysplastic syndromes) or do not display (myeloproliferative neoplasms) significant dysmyelopoiesis :
●The myelodysplastic syndromes (MDS) are characterized by dysplastic bone marrow hyperplasia or even occasional hypoplasia, associated with variable degrees of peripheral blood cytopenia with or without monocytosis . The paradox between the proliferative bone marrow and the cytopenic peripheral blood picture in the MDS may be explained by increased intramedullary myeloid precursor cell apoptosis .