Breast cancer incidence among atomic-bomb survivors, 1950-2005

Summary

Several breast cancer incidence studies based on the RERF Life Span Study (LSS) population were conducted during the period from 1950 through 1990. Among those breast cancer cases, a highly significant linear dose response was observed in breast cancer incidence among exposed people; among women exposed at less than 20 years of age, excess relative risk per Sv for those with attained age of 35 or more was around 2, whereas excess relative risk per Sv for those with attained age of 20 years or more and less than 35 was shown to be remarkably high, at 16.8. Further, among women exposed at less than 20 years of age, excess relative risk of bilateral breast cancer per Sv was also shown to be high, which suggested the presence among them of a group highly sensitive to radiation-induced carcinogenesis. However, more recent data indicate that both age at exposure and attained age are important modifiers of the radiation-related risk of breast cancer, and the relative importance of these two factors is dependent on models, background rates, and other assumptions used. We thus need to pursue the risk analysis to better understand the risk patterns in an extended follow-up and try to identify morphological or other features contrasting early- vs. late-onset breast tumors. In this study, we will examine new breast cancer cases occurring in the LSS population during the 15 years (from 1991 through 2005) following the previous period and cases that occurred during the previous study period but were registered after that period. Ages at diagnosis of new breast cancer cases occurring during the period from 1991 through 2005 are at least 45 years old. We will examine new findings and compare them with previous findings, and review all breast cancer cases during the entire period since the previous study, by classifying them based on new criteria of the World Health Organization (WHO) histological classification.

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