Malignant transformation of monoclonal gammopathy of undetermined significance: Cumulative incidence and prognostic factors

The cumulative incidence of malignant transformation was studied in 88 patients with monoclonal gammopathy of undetermined significance (MGUS) that had a complete prospective follow-up. At a median follow-up of 6.75 years, 10 patients developed multiple myeloma (MM) (11.4 %) and 2 developed inimunocytoma (2.3 %). The cumulative incidence of malignant transformation was 9.1, 21.3, 38 and 48.3 % at 5, 10, 15 and 20 years, respectively. In univariate analysis on 102 MGUS patients., M-component level, bone marrow plasma cell percentage and kappa light chain correlated significantly with the development of a malignancy (p=0.0289, 0.0265 and 0.0013, respectively), In multivariate analysis, light chain type of M-component and plasma cell percentage had independent prognostic significance. A high-risk (M-component level > 10 g/l and/or plasma cell percentage > 2 %) and a low-risk group ( M-component level < 10 g/l and/or plasma cell percentage < 2 %) of MGUS patients was identified, which differed significantly in the cumulative incidence of developing a malignancy (p <0.001 for M-component level and p=0.007 for plasma cell percentage). These results imply that high-risk patients should receive a more frequent follow-up, in comparison to low-risk patients.