In another study, MGUS patients with none, 1, or 2 of the following risk factors, >95% of bone marrow plasma cells that are clonal in nature and a 10% or greater rise in the levels of their monoclonal proteins within 3 years, had 2, 16, and 72% risks, respectively, of progression within 7 years. However, estimates on the risks of progression for some of these parameters are tentative and subject to change. For example, the IgA form of MGUS, while once considered to have a poorer prognosis than IgG MGUS, was found to have a prognosis similar to IgG MGUS in a more recent study. IgM MGUS
While traditionally classified as such, it is not clear that IgM MGUS is a clonal plasma cell dyscrasia. IgM MGUS involves an increase in a B cell derivative with morphological features of both plasma cells and lymphocytes viz., lymphoplasmacytic  cells. Studies indicate that both plasma cells and lymphoblastic cells infiltrate involved tissues and that one or perhaps both cell types harbor mutations in a) the MYD88 gene (~20% in IgM MGUS and >90% in IgM-related malignancies), almost all of which are L265P mutations (i.e.
These cases should have no symptoms or findings of end organ dysfunction attributed to Waldenström macroglobulinemia such as anemia, decreases in any white blood cell count, cold agglutinin disease, hyperviscosity of blood, lymphadenopathy, hepatomegaly, splenomegaly, peripheral neuropathy, cryoglobulinemia, or constitutional symptoms.As determined by a Mayo Clinic study of 48 individuals, smoldering Waldenström macroglobulinemias risk of progression to Waldenström macroglobulinemia is estimated to be ~12% per year and then falling of sharply for at least the next 5 years to 2% per year. In this study the only factor predictive of a more rapid progress was a finding of anemia (hemoglobin level <115 grams/liter). During a 15-year follow-up, the Clinic subsequently reported that patients progressed to Waldenström macroglobulinemia, amyloidosis, or a related IgM-associated neoplasm at a rate of 6%, 39%, 59%, and 68% after the first, third, fifth, and tenth year, respectively. However, the Southwest Oncology Group in a study on 231 individuals reported that the smoldering disease progressed to overt Waldenström macroglobulinemia over 9 years in only 26% of cases. Light chain SMM
Light chain smoldering multiple myeloma (light chain SMM) was previously termed idiopathic Bence Jones proteinuria. The condition is currently diagnosed in asymptomatic individuals who have a 24-hour urinary Bence Jones, i.e. light chain myeloma protein level, that is >0.5 grams and/or bone marrow plasma cells that are 10% to <60% of nucleated cells.