Monoclonal gammopathy of undetermined significance in atomic bomb survivors: incidence and transformation to multiple myeloma

Among 6737 atomic bomb survivors who did not have monoclonal gammopathy at the first examination, 112 developed monoclonal gammopathy of undetermined significance (MGUS) between 1985 and 2001. The crude incidence rate was 164 per 100 000 person-years in the overall study population, with a sharp increase in incidence after age 60 years. The incidence was not significantly associated with radiation dose (P = 0.91), although the incidence at less than 80 years of age showed a marginally significant association (P = 0.05). Among 75 patients with MGUS detected in 1985, 50 patients (67%) had died by 2001, 16 (21%) of these deaths were due to multiple myeloma (MM). MM mortality among MGUS patients was 2284 per 100 000 person-years while the rate in the total population was 14.6 per 100 000 person-years. The risk of MM mortality was greater in the older generation. The transformation from MGUS to MM was faster in exposed persons than in non-exposed persons, but this was not statistically significant.