Chronic myelomonocytic leukemia: 2018 update on diagnosis, risk stratification and management

Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic stem cell disorder with overlapping features of myelodysplastic syndromes and myeloproliferative neoplasms, with an inherent risk for leukemic transformation (∼15%-20% over 3-5 years).

Diagnosis is based on the presence of sustained (>3 months) peripheral blood monocytosis (≥1 × 10⁹ /L; monocytes ≥10%), along with bone marrow dysplasia. Clonal cytogenetic abnormalities occur in ∼ 30% of patients, while >90% have gene mutations. Mutations involving TET2 (∼60%), SRSF2 (∼50%), ASXL1 (∼40%) and the oncogenic RAS pathway (∼30%) are frequent; while the presence of ASXL1 and DNMT3A mutations and the absence of TET2 mutations negatively impact over-all survival.

Molecularly integrated prognostic models include; the Groupe Français des Myélodysplasies (GFM), Mayo Molecular Model (MMM), and the CMML specific prognostic model (CPSS-Mol). Risk factors incorporated into the MMM include presence of nonsense or frameshift ASXL1 mutations, absolute monocyte count > 10 × 10⁹ /L, hemoglobin <10 gm/dL, platelet count <100 × 10⁹ /L and the presence of circulating immature myeloid cells. The MMM stratifies CMML patients into 4 groups; high (≥3 risk factors), intermediate-2 (2 risk factors), intermediate-1 (1 risk factor), and low (no risk factors), with median survivals of 16, 31, 59, and 97 months, respectively.

Hypomethylating agents such as 5-azacitidine and decitabine are commonly used, with overall response rates of ∼30%-40% and complete remission rates of ∼7%-17%; with no impact on mutational allele burdens. Allogeneic stem cell transplant is the only potentially curative option, but is associated with significant morbidity and mortality.