Chronic myelomonocytic leukemia (CMML)

Chronic myelomonocytic leukemia (CMML) is an aggressive, clonal bone marrow disorder that induces a persistent monocytosis and in some cases an accumulation of dysplastic granulocytes at various stages of maturation. Because of the combination of monocyte accumulation with myelodysplastic features, the disease is classified by the WHO as an overlap, myelodysplastic syndrome (MDS)/myeloproliferative neoplasm (MPN). The disease annual incidence, ranging between 0.35 and 0.52/10⁵ population in Western countries, may be underestimated as low-risk forms are commonly neglected. CMML is a disease of aging whose median age at diagnosis is 72 years, with a male/female predominance of approximately 2:1 whose origin remains unclear. The disease is infrequent before 50 years, except on the basis of germline alterations, and prognosis could be less severe in these younger patients, probably because younger patients present with fewer comorbidities and are more often eligible for allogeneic stem cell transplantation. Clonal hematopoiesis of indeterminate potential (CHIP), as defined by the occurrence of clonal mutations in otherwise healthy individuals, may be a first step to CMML. In 15–30% of cases, the chronic disease transforms into acute myeloid leukemia (AML). Even in the absence of transformation, the disease outcome is poor with a median overall survival ranging between 16 and 30 months, depending on the series.