Women from Hiroshima and Nagasaki who had their first periods around the time of the atomic bombs are at an increased risk of developing breast cancer, a study has found.
The findings by researchers from Japan and the United States were released by the Radiation Effects Research Foundation (RERF) on Oct. 15, and published in the U.S. academic journal Radiation Research in the same month.
Past studies have revealed patients have a higher risk of breast cancer when they start menstruating earlier or receive doses of radiation in their early years.
Alina V. Brenner, a senior scientist at RERF, said the correlation between onset of menstruation and radiation exposure ages and the radiation-derived risk suggests breast tissue is more sensitive to radiation around the emergence of secondary sexual characteristics.
In the latest study, RERF tracked 120,000 hibakusha atomic bomb survivors and non-hibakusha, and analyzed radiation doses received and the ages of women suffering from breast cancer when they had their first period.
With 11 additional years of follow-up, the number of female breast cancer cases increased by 397 (or 37%) since the previously reported analysis (3). Most new cases were among females exposed before age 20, increasing statistical power to address long-term effects of radiation exposure at young ages. We continue to find a strong breast cancer dose response consistent with linearity. The ERR per Gy remained stable as analyses were limited to successively lower dose ranges down to 0.250 Gy. The ERR was significantly modified by attained age, with the estimated ERR per Gy of 1.12 for a 70-year-old female after exposure at age 30 without allowance for effect modification by age-at-menarche, which was similar to the previously reported estimate (3). In addition, age at menarche had an independent modifying effect on the ERR (24% decrease in the ERR per year increase in age at menarche); the ERR at 1 Gy for a female at attained age 70, with age at menarche of 15 and exposure at age 30, was 1.04. In absolute risk, the EAR increased with increasing attained age up to age 70 and then declined slightly, reflecting the age pattern of baseline rates in females. Age at menarche was also a significant modifier of the EAR (29% decrease in the EAR per year increase in age at menarche). Additional analyses suggested a non-monotonic pattern of the ERR and EAR by age at exposure before compared to after menarche (see further discussion below).