Cytopenia, Dysplasia, and Monocytosis: A Precursor To Chronic Myelomonocytic Leukemia or a Distinct Subgroup? Case Reports and Review of Literature

Chronic myelomonocytic leukemia (CMML) consists of disorders with overlapping dysplastic and proliferative features. The diagnosis of CMML requires absolute monocytosis (> 1000/μL) in addition to other criteria outlined by the World Health Organization (WHO) classification.1 Monocytosis not reaching 1000/μL has been observed in myelodysplastic syndrome (MDS) and presents a diagnostic challenge in classification especially if increases in leukocyte count occurring during disease shifts the monocyte count into the absolute range. We discuss the laboratory and clinical features of 3 patients with myelodysplasia and associated monocytosis. Absolute neutropenia was the dominant feature at presentation, with mild anemia, thrombocytopenia, monocytosis (as a percentage), multilineage dysplasia, and increased myeloblasts, consistent with a diagnosis of refractory anemia with excess blasts (RAEB). Absolute monocytosis fulfilling the diagnostic criteria for CMML developed over 6-8 months, prompting a change in diagnosis. Two of 3 patients had normal cytogenetic examinations. JAK2 V617F mutation was detected after transformation to CMML in 1 of them; in the other, a novel translocation t(5;12)(p13;q24) was observed at the time of progression to acute leukemia. The use of different diagnostic terminologies—MDS, dysplasia with reactive monocytosis, myeloproliferative, and myeloproliferative/myelodysplastic syndromes by different and even the same pathologists at different times created confusion among the clinicians and patients.The disease course in these 3 patients was characterized by better survival and prolonged time to progression to acute leukemia, than predicted based on the original diagnosis of RAEB, suggesting that MDS with monocytosis may represent a subgroup distinct from MDS or CMML.