Chronic myelomonocytic leukemia and myelodysplastic syndrome/myeloproliferative overlap syndromes

Practicing hematologists and hematopathologists have long recognized that patients with myelodysplastic syndromes (MDS) typically present with cytopenia(s), and those with chronic myeloproliferative disorders (CMPD) typically present with elevated blood counts and organomegaly, but there are also patients who have clinical, laboratory, and/or pathologic features of both MDS and CMPD, and those patients are not easily assigned to either category. Thus, prior to the publication of the World Health Organization (WHO) classification of hematopoietic neoplasms (see chaps. 1 and 9), some patients with left-shifted neutrophilia and absolute monocytosis and morphologic features of dysgranulopoiesis were classified as chronic myelomonocytic leukemia (CMML) under the family of MDS, whereas others who also had left-shifted neutrophilia and morphologic features of dysgranulopoiesis but less monocytosis were classified as atypical chronic myeloid leukemia (aCML) under the CMPD umbrella.