IgM monoclonal gammopathy of undetermined significance (MGUS) and smoldering Waldenström's macroglobulinemia (SWM).

Monoclonal gammopathy of undetermined significance of IgM class (IgM MGUS) was diagnosed in 213 Mayo Clinic patients who were residents of 11 counties in Southeastern Minnesota from 1960 to 1994. During long-term follow-up 29 (14%) developed non-Hodgkin lymphoma (n=17), Waldenström's macroglobulinemia (n=6), chronic lymphocytic leukemia (n=3), and AL amyloidosis (n=3) with relative risks of 15-, 262-, 6-, and 16-fold, respectively. The cumulative probability of progression to one of these disorders was 10% at 5 years, 18% at 10 years, and 24% at 15 years, approximately 1.5% per year.Forty-eight patients with SWM were identified at Mayo Clinic from 1974 to 1995. During 285 cumulative person-years of follow-up (median, 15.4 years) 34 (71%) progressed to Waldenström's macroglobulinemia (WM), 1 to AL amyloidosis, and 1 to lymphoma (total, 36 [75%]). The cumulative probability of progressing to WM, amyloidosis, or lymphoma was 6% at 1 year, 39% at 3 years, and 59% at 5 years (12% per year).