Characteristics and prognosis of patients with non-immunoglobulin-M monoclonal gammopathy of undetermined significance: a retrospective study.

Non-immunoglobulin (Ig)-M monoclonal gammopathy of undetermined significance (MGUS) is a precursor lesion with the potential to evolve into a malignant plasma cell neoplasm. The prevalence of MGUS differs by ethnicity and is lower in the Japanese population than in the Western population. However, there is limited evidence about the clinical course of MGUS in Asian races. The present study aims at elucidating the clinical course and prognosis of Japanese patients with non-IgM MGUS in the clinical setting. We retrospectively examined 1009 patients with non-IgM MGUS identified by screening procedures. The median overall survival of these patients was > 20 years, and only one-fifth patients died of plasma cell neoplasms. The cumulative incidence of plasma cell neoplasms requiring treatment was 19%. Multivariate analysis revealed that immunoparesis and female gender were independent factors affecting treatment requirement. Although the characteristics and clinical course of patients with non-IgM MGUS obtained in this study were found to be essentially similar to those of previous studies, we report here for the first time that female gender is a significant independent factor for requiring treatment.