Although exposure to ionizing radiation is a recognized risk factor for breast cancer, the potential hazard from low-dose, fractionated exposures during early breast development has not been thoroughly evaluated. Women with scoliosis represent a valuable population for studying this issue because they are exposed to multiple diagnostic x rays during childhood and adolescence, times when the breast may be highly sensitive to the carcinogenic effects of radiation. A study was conducted of 1,030 women with scoliosis who were seen at four Minneapolis area medical facilities between 1935 and 1965. The average age at diagnosis was 12.3 years; 60% of the women had idiopathic scoliosis. Individual x-ray films were counted and the number per patient ranged from 0 to 618 films (mean, 41.5). On average, the x-ray exposures were given over an 8.7-year period. Ninety percent of the women were located, of whom over 92% responded to a mail questionnaire or telephone interview. The average period of observation was 26 years. Overall, 11 cases of breast cancer were reported, compared with six expected (standardized incidence ratio = 1.82, 90% confidence interval = 1.0-3.0). Excess risk increased with time since exposure and was highest among those followed for more than 30 years (standardized incidence ratio = 2.4). Risk also increased with the number of x rays and with the estimated radiation dose to the breast (mean, 13 rad). These data suggest that frequent exposure to low-level diagnostic radiation during childhood or adolescence may increase the risk of breast cancer. [J Natl Cancer Inst 81:1307-1312, 1989].
Bibliographical noteFunding Information:
Received January 12, 1989; revised May 31, 1989; accepted June 19, 1989. Supported in part by Public Health Service contracts N01-CP3-1036, N01-CP6-1006, and N01-CP0-1047 from the National Cancer Institute, National Institutes of Health, Department of Health and Human Services; the Scoliosis Research Society; the Twin Cities Scoliosis Research Fund; and the Medical Education and Research Foundation of Gillette Children's Hospital, St. Paul, MN. D. A. Hoffman, Centers for Disease Control, Atlanta, GA. J. E. Lonstein, Minnesota Spine Center, Minneapolis, MN. M. M. Morin, J. D. Boice, Jr., Radiation Epidemiology Branch, Epidemiology and Biostatistics Program, National Cancer Institute, National Institutes of Health, Bethesda, MD. W. Visscher, B. S. H. Harris III, Research Triangle Institute, Research Triangle Park, NC. We thank Marilyn Stovall for expert advice and organ dose estimates, Cathy Drzyzgula for computer assistance, and the staffs of the participating hospitals and medical facilities. *Correspondence to: Dr. John D. Boice, Jr., Radiation Epidemiology Branch, National Cancer Institute, Executive Plaza North, Suite 408, Bethesda, MD 20892.