Introduction

The myeloproliferative disorders (MPDs) comprise polycythemia vera (PV), essential thrombocythemia (ET) and idiopathic myelofibrosis (IMF). They were first classed together as an overlapping spectrum of preleukemic disorders along with chronic myeloid leukemia (CML) by Dameshek in 1951. CML, with its pathognomonic chromosomal translocation, greater clinical homogeneity and increased acute leukemic potential, is now considered a separate entity. The MPDs are believed to result from acquired genetic changes in hemato-poietic stem cells that perturb stem cell behavior and result in the overproduction of one or more myeloid lineages. These disorders are not mutually exclusive and considerable overlap is seen between distinct categories, with progression from one disease to another a frequent occurrence (Figure 9.1). The MPDs are also preleukemic and a small proportion of patients transform to acute myeloid leukemia (AML).

Fig. 9.1 Relationships of the myeloproliferative disorders and transformation to acute myeloid leukemia

The percentage of patients who transform varies according to the initial disease, duration of disease and treatment. HSC, hematopoietic stem cell; PV, polycythemia vera; IMF, idiopathic myelofibrosis; ET, essential thrombocythemia; AML, acute myeloid leukemia.

Fig. 9.1 Relationships of the myeloproliferative disorders and transformation to acute myeloid leukemia

The percentage of patients who transform varies according to the initial disease, duration of disease and treatment. HSC, hematopoietic stem cell; PV, polycythemia vera; IMF, idiopathic myelofibrosis; ET, essential thrombocythemia; AML, acute myeloid leukemia.

The MPDs are relatively uncommon disorders. PV has an annual incidence of 5-10 cases per million population. Less is known about the incidence of ET. However, it is likely to be similar to, if not greater than, that for PV. Although little is known of the epidemiology of IMF, it is thought to have an incidence of 5 cases per million population annually but, since many patients are diagnosed coincidentally and up to 25% are asymptomatic at the time of diagnosis, this figure is likely to be an underestimate.

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