Essential thrombocythemia (ET) is a myeloproliferative neoplasm (MPN) that mainly affects middle-aged patients. Although pediatric cases occur, they are rare, and their molecular features considerably differ from the adult counterparts: JAK2V617F mutation occurs in only 25% of cases,1 CALR mutations are found in <10% of patients,2 and the MPLW515L mutation is anecdotal.3 Overall, <40% of children with unexplained, long-lasting thrombocytosis have a clonal marker of ET.2
After the release of the 2001 World Health Organization (WHO) classification,4 bone marrow (BM) evaluation has become a cornerstone of ET diagnosis. However, the majority of studies has focused on adults, and little is known about the role of BM biopsy in pediatric ET. In fact, BM biopsy is seldom performed in children with a clinical picture of ET due to the invasiveness of the procedure. The main objective of this study was to explore the relevance of BM histology in children with high platelet counts in order to identify possible differences in: (1) primary vs reactive/secondary thrombocytosis (PedST) of childhood; and (2) pediatric (PedET) vs adult (AdET) cases of ET.