A case-control interview study of breast cancer among Japanese A-bomb survivors. II. Interactions with radiation dose.
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.
Land
C E
CE
National Cancer Institute, Bethesda, MD.
Hayakawa
N
N
Machado
S G
SG
Yamada
Y
Y
Pike
M C
MC
Akiba
S
S
Tokunaga
M
M
D000328:Adult; D000367:Age Factors; D000368:Aged; D001943:Breast Neoplasms / Q000453:epidemiology*; D016022:Case-Control Studies; D015331:Cohort Studies; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D007407:Interviews as Topic; D007564:Japan / Q000453:epidemiology; D007774:Lactation; D008423:Maternal Age; D008875:Middle Aged; D009689:Nuclear Warfare; D010298:Parity; D017698:Postmenopause; D017697:Premenopause; D011829:Radiation Dosage; D012307:Risk Factors; D013534:Survival