BCR and primary myelofibrosis: In contrast to the adult population, the classical BCR::ABL1-negative myeloproliferative neoplasms (BCR::ABL1-neg MPNs), i.e. polycythaemia vera (PV), essential thrombocythaemia (ET) and primary myelofibrosis (PMF) [1] are very rare in the paediatric population with an incidence approximately 100×lower than in adults [2].