Kyle RA, et al. - Researchers analyzed the long-term follow-up of monoclonal gammopathy of undetermined significance (MGUS) in patients who resided in southeastern Minnesota. They found significant differences in the risk of progression between patients with IgM MGUS and those with non-IgM MGUS. Among patients with MGUS, overall survival was shorter than was expected in a matched control population.

Methods

• This study included 1,384 patients who were residing in southeastern Minnesota and in whom MGUS was diagnosed at the Mayo Clinic during 1960-1994.
• The median follow-up was 34.1 years (range, 0.0 to 43.6).
• The progression to multiple myeloma or another plasma-cell or lymphoid disorder was the primary endpoint.

Results

• MGUS progressed in 147 patients (11%) during 14,130 person-years of follow-up, which was 6.5 times (95% confidence interval [CI], 5.5 to 7.7) as high as the rate in the control population.
• Without accounting for death due to competing causes, the risk of progression was 10% at 10 years, 18% at 20 years, 28% at 30 years, 36% at 35 years, and 36% at 40 years.
• The presence of 2 adverse risk factors among patients with IgM MGUS [namely, an abnormal serum free light-chain ratio (ratio of kappa to lambda free light chains) and a high serum monoclonal protein (M protein) level (≥1.5 g per deciliter] was correlated with a risk of progression at 20 years of 55%, as compared with 41% among patients who had 1 adverse risk factor and 19% among patients who had neither risk factor.
• The risk of progression at 20 years was 30% among those who had the 2 risk factors, 20% among those who had 1 risk factor, and 7% among those who had neither risk factor, among patients with non-IgM MGUS.
• Survival was shorter among patients with MGUS than was expected in the control population of Minnesota residents of matched age and sex (median, 8.1 vs 12.4 years; P<0.001).