Chronic neutrophilic leukemia and chronic myelomonocytic leukemia: WHO defined

The World Health Organization (WHO) classification of myeloid disorders has provided updated parameters for the consistent diagnosis of two previously less than optimally defined chronic myeloid disorders, CNL and CMML. The classification of these disorders, which had been controversial, is now better defined and provides more clinically and biologically relevant disease definitions to enable uniform diagnosis and a framework to evaluate natural history and therapeutic interventions. CNL is now recognized as a distinct entity among the chronic myeloproliferative disorders and CMML is included within the new category of ‘myelodysplastic/myeloproliferative diseases’ (MDS/MPD). Predominant neutrophilia defines CNL whereas CMML is defined by predominant and monocytosis. In each case these defining features must be distinguished from reactive causes for the same in the absence of clear evidence of myeloid clonality (CNL and CMML) or dysplasia (CMML). The exclusion of underlying bcr/abl-driven oncogenesis is an essential component in the diagnosis of these chronic leukemic processes. The optimal therapy for both CNL and CMML remains uncertain. Current management decisions are based on small studies or extrapolated from therapeutic strategies that are effective in similar chronic, clonal myeloid disorders. Given the potential for evolution to acute leukemia or progressive refractory leucocytosis or cytopenias, allogeneic stem cell transplantation might be appropriate for younger patients. Continued reporting and investigation of specific therapeutic strategies and responses must be encouraged.