Bone marrow failure in childhood: central pathology review of a nationwide registry

Refractory cytopenia of childhood (RCC) was proposed as a provisional entity in the 2008 WHO classification of myelodysplastic syndromes (MDS). It is defined as a childhood MDS featuring persistent cytopenia without increase blasts in bone marrow (BM) or peripheral blood (PB). Because the majority of RCC cases feature hypocellularity and pancytopenia, it is quite challenging to differentiate RCC from acquired aplastic anemia (AA) and many kinds of inherited bone marrow failure syndromes (IBMFS). Diagnosis of RCC requires BM histology of characteristic features such as isolated erythroid islet with left shift, abnormal localization and micromegakaryocytes. The Japanese Society of Pediatric Hematology/Oncology has opened the central registry review system since 2009 to evaluate childhood cases of bone marrow failure (BMF). It has reviewed cytology and BM pathology of all registered BMF cases, which number more than 1,700. In the evaluation of BMF, BM pathology is important to assess the mechanism of hematopoiesis. Pathological dysplasia should be differentiated from cytological dysplasia. A central review system is important for rare diseases, such as pediatric BMF. Standardization of pathological diagnosis should be established upon consensus findings, descriptions, and diagnostic approaches. In this review, the pathology of pediatric BMF syndromes is summarized.