IntroductionMonoclonal gammopathy of undetermined significance (MGUS) is a premalignant condition with a risk of malignant conversion. Patients and methodsWith the aim to estimate the cumulative risk MGUS progression to hematologic malignancies, we analyzed a nationwide population-basedcohort of 1887 MGUS patients from the Czech Registry of Monoclonal Gammopathies (RMG) between 2007 and 2013. ResultsDuring the follow-up period (median 4years; range 0.6-34.8), progression to hematologic malignancies was observed in 8.6% (162 of 1887) of patients. Factors associated with progression were as follows: M-protein concentration 1.5g/dL, pathological sFLC (<0.26 or >1.65) ratio, bone marrow plasma cells (BMPCs) in cytology >5%, immunoparesis, age 69years, and the level of serum hemoglobin at baseline <12.0g/dL. Combining these factors, we propose a new risk model (CMG model). The risk of progression at 10years was 1.6%, 16.9%, 22.9%, 39.4%, and 52.3%, respectively, if 0 (reference group), one, two, three, or four to five risk factors are present (P<.001) with HR 63 times higher compared to the reference MGUS group. ConclusionThe new CMG model was established with an advantage for better identification of MGUS patients at low risk.