Epidemiology of Myelodysplastic Syndromes in Atomic Bomb Survivors

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[Background] Myelodysplastic syndromes (MDS) are acquired clonal stem cell disorders characterized by ineffective hematopoiesis and a high risk of progression to leukemia. Etiologies of MDS are still unknown. So far, there is no large-scale epidemiological study for population exposed to radiation.[Aim] To investigate the association between radiation exposure and a risk of MDS in Atomic bomb survivors.[Methods] Overall MDS cases were retrospectively accumulated from five hospitals in Nagasaki City and then identified Atomic bomb survivors by linkage with the Database of Nagasaki Atomic Bomb Survivors in the Scientific Data Center at Nagasaki University. Disease confirmation was conducted with the microscopic examination of bone marrow smear and clinical data. In retrospective cohort analyses, we set a retrospective cohort of Atomic bomb survivors who were alive at 1980.1.1 but no MDS. In age-adjusted population analyses, we used official prefecture population statistics and then compared MDS incidence between Atomic bomb survivors and Non-Atomic bomb survivors.[Results] Up to now, we accumulated approximately 600 MDS cases diagnosed during 1970' to 2004, and identified around 200 cases who were Atomic bomb survivors. In retrospective cohort analyses, 162 MDS were identified among a cohort of 87496 survivors during 1980 to 2004 (crude incidence rate: 10.7 per 103 PY). Risk of MDS was high in male than female (RR=1.7), in survivors exposed within 1.5km from hypocenter than those over 3.0km (RR=4.3). Risk of subtypes of RAEB ＆ RAEB-t was high compared with subtypes of RA ＆ RARS among survivors exposed within 1.5km. In age-adjusted population analyses, crude incidence rate of MDS was higher in Atomic bomb survivors than Non-Atomic bomb survivors (crude incidence rate: 10.0 vs. 6.49 per 106 PY, RR=1.5).[Discussion] Results suggest a clear association between radiation exposure and a risk of MDS. Radiation dose analysis is needed to confirm this association.