Myeloproliferative neoplasms in children

Myeloproliferative neoplasms (MPNs) are a group of clonal hematopoietic stem cell disorders characterized by aberrant proliferation of one or more myeloid lineages often with increased immature cells in the peripheral blood. The three classical BCR-ABL-negative MPNs are (1) polycythemia vera (PV), (2) essential thrombocythemia (ET), and (3) primary myelofibrosis (PMF), which are typically disorders of older adults and are exceedingly rare in children. The diagnostic criteria for MPNs remain largely defined by clinical, laboratory, and histopathology assessments in adults, but they have been applied to the pediatric population. The discovery of the JAK2 V617F mutation and, more recently, MPL and calreticulin (CALR) mutations are major landmarks in the understanding of MPNs. Nevertheless, they rarely occur in children, posing a significant diagnostic challenge given the lack of an objective clonal marker. Therefore, in pediatric patients, the diagnosis must rely heavily on clinical and laboratory factors and exclusion of secondary disorders to make an accurate diagnosis of MPN. This review focuses on the clinical presentation, diagnostic work up, differential diagnosis, treatment, and prognosis of the classical BCR-ABL-negative MPNs (PV, ET, and PMF) in children and highlights the key differences to the adult diseases. Particular attention will be given to pediatric PMF, as it is the only disorder of this group that is observed in infants and young children, and in many ways appears to be a unique entity compared to adult PMF.