A case-control interview study of breast cancer among Japanese A-bomb survivors. II. Interactions with radiation dose

Land CE, Hayakawa N, Machado SG, Yamada Y, Pike MC, Akiba S, Tokunaga M
Cancer Causes and Control 5(2):167-76, 1994

Summary

Three breast cancer risk factors were evaluated in terms of their interactions with radiation dose in a case-control interview study of Japanese A-bomb survivors. Cases and controls were matched on age at the time of the bombings and radiation dose, and dose-related risk was estimated from cohort rather than case-control data. Each factor–age at first full-term pregnancy, number of deliveries, and cumulative lactation period summed over births–conformed reasonably well to a multiplicative interaction model with radiation dose (the additive interactive model, in which the absolute excess risk associated with a factor is assumed to be independent of radiation dose, was rejected). An important implication of the finding is that early age at first full-term pregnancy, multiple births, and lengthy cumulative lactation are all protective against radiation-related, as well as baseline, breast cancer. Analyses by age at exposure to radiation suggest that, among women exposed to radiation in childhood or adolescence, a first full-term pregnancy at an early age following exposure may be protective against radiation-related risk.