Pathomorphological diagnosis of <i>Ph</i>-negative chronic myeloproliferative neoplasms in children

BCR::ABL/Ph-negative chronic myeloproliferative neoplasms (CMPN) in children differ from those in adults in clinical manifestations and genetic alterations. Taking into account the well-known physiology of hematopoiesis in children, it seems important to compare the histological features of CMPN in pediatric patients with the criteria for the diagnosis of these diseases in adults specified in the World Health Organization (WHO) classification. In pediatric practice, the interpretation of changes in hematopoiesis in patients with CMPN without any established driver mutation has a particular importance for differential diagnosis with secondary thrombocytosis and erythrocytosis. For our analysis, we used bone marrow trephine biopsy specimens from the biobank of the Pathology Department of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology of Ministry of Healthcare of the Russian Federation. They had been obtained between 2016 and 2023 from 70 patients for initial histological examination. The final clinical diagnosis for these patients was CMPN. The frequency of the most common histological changes in hematopoiesis was assessed retrospectively. We compared our results with the data from the WHO classification, analysed the differences in morphological changes in the subgroups of patients with essential thrombocythemia with an established mutation or without it, assessed the relationship between the morphological changes and clinical symptoms of CMPN. The changes in hematopoiesis in children with CMPN are predominantly similar to those in adults, however there are differences in the morphology of megakaryocytes (scarcity of giant cells with hypersegmented nuclei (staghorn-like), an increased number of small and naked nuclei cells). In addition, bone marrow cellularity assessment has a low diagnostic value in differentiating between essential thrombocythemia and polycythemia vera in children. There are no differences in morphology in the subgroups of patients with essential thrombocythemia with an established mutation or without it. No statistically significant association between clinical symptoms of the disease and any of the morphological features of CMPN was found. The study was approved by the Independent Ethics Committee and the Scientific Council of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology of Ministry of Healthcare of the Russian Federation.