The production and deployment of phagocytes are central functions of the hematopoietic system. In the 1950s, radioisotopic studies demonstrated the high prodution rate and short lifespan of neutrophils and allowed researchers to follow the monocytes as they moved from the marrow through the blood to become tissue macrophages, histiocytes, and dendritic cells. Subsequently, the discovery of the colony-stimulating factors greatly improved understanding the regulation of phagocyte production.

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Severe chronic neutropenia (SCN) is defined as an absolute neutrophil (ANC) of less than

SummaryIn severe congenital neutropenia (SCN), long‐term therapy with granulocyte colony‐stimulating factor (G‐CSF) has reduced mortality from sepsis, revealing an underlying predisposition to myelodysplastic syndrome and acute myeloid leukaemia (MDS/AML). We have reported the early pattern of evolution to MDS/AML, but the long‐term risk remains uncertain. We updated a prospective study of 374 SCN patients on long‐term G‐CSF enrolled in the Severe Chronic Neutropenia International Registry. Long‐term, the annual risk of MDS/AML attained a plateau (2·3%/year after 10 years). This risk now appears similar to, rather than higher than, the risk of AML in Fanconi anaemia and dyskeratosis congenita.