Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic stem cell disorder associated with peripheral blood monocytosis, with an inherent risk for leukemic transformation. CMML has overlapping features of myelodysplastic syndromes (MDS) [DS:H01481] and myeloproliferative neoplasms (MPN). Gene mutations are seen in >90% of patients, with common abnormalities involving; epigenetic regulators (TET2 -60% and ASXL1 -40%), spliceosome components (SRSF2 -50%), transcription factors (RUNX1 -15%) and cell signaling (RAS -30%, CBL -15%).