An evolutionary perspective on chronic myelomonocytic leukemia

Chronic myelomonocytic leukemia (CMML) shares with other myeloid diseases a number of somatic gene mutations. These mutations can now be integrated within the framework of evolution theory to address the mechanisms of the disease. Several evidences indicate that the disease emerges in adult hematopoietic stem cells (HSC) through the age-dependent accumulation of DNA damage, leading stochastically to a driver mutation that confers a competitive advantage to the cell. A mutation in TET2 gene could be one of these driver mutations provoking the emergence of clonality. After a long latency, secondary lesions, such as mutations in the SRSF2 gene, contribute to progression to full-blown malignancy, with abnormal differentiation. Additional mutations accumulate and branching arising mostly through mitotic recombination generates clonal heterogeneity. Modifications in the microenvironment probably affect this clonal dynamics, whereas epigenetic alterations, such as hypermethylation of the TIF1γ gene promoter, may generate phenotypic diversification of otherwise clonal populations. The preserved although deregulated myeloid differentiation that characterizes CMML, with granulomonocyte expansion and various cytopenias, may depend on early clonal dominance in the hematopietic cell hierarchy. Progression to acute myeloid leukemia observed in 25-30% of the patients may arise from the massive expansion of a clone with novel genetic lesions, providing a high fitness to previously minor subclones when in chronic phase of the disease. This review discusses the various models of disease emergence and progression and how this recent knowledge could drive rational therapeutic strategies.