Introduction

Although hematologic malignancies are collectively the most common neoplasms of childhood, comprising approximately one-fourth to one-third of all cases of pediatric cancer in the USA, the myeloproliferative neoplasms, formerly termed chronic myeloproliferative disorders, are distinctly rare in the pediatric setting [1, 2]. Among the seven entities recognized by the 2008 WHO classification of myeloproliferative neoplasms (Table 12.1), chronic myelogenous leukemia and mastocytosis are the only ones encountered with any regularity in the pediatric population. Primary myelofibrosis, polycythemia vera, and essential thrombocythemia are very uncommon in children, and chronic neutrophilic leukemia and chronic eosinophilic leukemia are extraordinarily rare in this population, the description of which is limited to an occasional case report [3]. Several pediatric “myeloproliferative” disorders are not truly neoplastic, and as such they have a pathogenesis distinct from their bona fide neoplastic counterparts in adults. The application to these pediatric disorders of the same terminology employed for adult myeloproliferative neoplasms, which are by definition clonal and neoplastic, creates confusion with regard to their pathogenesis, clinical behavior, and appropriate treatment. Our discussion of pediatric myeloproliferative neoplasms will focus almost exclusively on those disorders seen in children, with emphasis on the distinctive aspects of the pediatric forms of these disorders, as well as conditions which can mimic true pediatric myeloproliferative neoplasms. Myeloproliferative neoplasms which are exceedingly rare in children (e.g., chronic neutrophilic leukemia) will not be discussed.