To describe myelodysplastic syndrome (MDS)/myeloproliferative neoplasm (MPN) combined with monoclonal gammopathy of undetermined significance (MGUS) in order to investigate the potential association between these 2 diseases. Two cases of confirmed chronic myelomonocytic leukemia (CMML) combined with MGUS were reported. In addition, prior publications of cases with combined MDS or MPN with MGUS were reviewed. The first case was of a 77-year-old man whose routine blood tests showed abnormal hemogram results. The diagnosis was CMML combined with IgM monoclonal gammopathy, and the disease course was 4 years. The CMML gradually progressed and the patient presented with anemia, thrombocytopenia, autoimmune hemolysis, and an increase in the number of immature cells in the bone marrow. Although the MGUS caused fluctuations in the concentrations of IgM, no IgM-associated organ damage was observed. Eventually, this patient died from a lung infection. The second case was of a 78-year-old man who sought treatment because of fever and a cough. An increase in the number of monocytes was discovered in the peripheral blood. Bone marrow smear results suggested obvious active granulocytes and an increase in the percentages of promyelocytes, myelocytes, and metamyelocytes. Unhealthy granulocytes and immature monocytes could also be observed, and the percentage of monocytes was increased. In addition, serum IgG levels were increased, and immunofixation electrophoresis results showed IgG-κ type M proteins. The diagnosis was CMML combined with IgG monoclonal gammopathy. These diseases were stable and follow-up was conducted for 1 year after diagnosis. The cases in this study combined with those that were reviewed in the relevant literature indicate that the presence of these 2 diseases in the same patient might not be a coincidence. The development of the 2 diseases in case 1 was different, and we speculate that they might have had different clonal origins. Whether CMML is a risk factor for MGUS and the role of clonal plasma cells in the occurrence and development of MDS and MDS/MPN requires further studies on a larger number of cases.
