Probability of progression in 213 patients. Patients were residents of southeastern Minnesota in whom monoclonal gammopathy of undetermined significance (MGUS) of IgM class was diagnosed from 1960 through 1994. Curve shows probability of progression of MGUS to lymphoma, Waldenström macroglobulinemia, primary amyloidosis, or chronic lymphocytic leukemia. Bars show 95% confidence intervals. Numbers at bottom of the horizontal axis are numbers of patients at risk at each interval.