BCR and myeloproliferative neoplasm: The rarity of BCR::ABL1-neg MPNs in children and adolescents severely limits the opportunities to perform clinical studies on these malignancies in paediatric population, and as a consequence, in contrast to the adult population, there are still no established specific diagnostic and prognostic criteria and clear treatment recommendations based on these criteria, including indications for allo-HCT in paediatric patients suffering from BCR::ABL1-neg MPN.