Breast cancer mortality after diagnostic radiography - Findings from the US Scoliosis Cohort Study

Study Design. A retrospective cohort study was conducted in 5573 female pat ients with scoliosis who were referred for treatment at 14 orthopedic medic al centers in the United States, Patients were less than 20 years of age at diagnosis which occurred between 1912 and 1965. Objectives. To evaluate patterns in breast cancer mortality among women wit h scoliosis, with special emphasis on risk associated with diagnostic radio graph exposures. Summary of Background Data. A pilot study of 1030 women with scoliosis reve aled a nearly twofold statistically significant increased risk for incident breast cancer. Although based on only 11 cases, findings were consistent w ith radiation as a causative factor. Methods. Medical records were reviewed for information on personal characte ristics and scoliosis history. Diagnostic radiographic exposures were tabul ated based on review of radiographs, radiology reports in the medical recor ds, radiograph jackets, and radiology log books. Radiation doses were estim ated for individual examinations. The mortality rate of the cohort through January 1, 1997, was determined by using state and national vital statistic s records and was compared with that of women in the general U.S. populatio n. Results. Nearly 138,000 radiographic examinations 'average number of examin ations per patient was 24.7 (range, 0-618); mean estimated cumulative radia tion dose to the breast was 10.8 cGy (range, 0-170). After excluding patien ts with missing information, 5466 patients were included in breast cancer m ortality analyses. Their mean age at diagnosis was 10.6 years and average l ength of follow-up was 40.1 years. There were 77 breast cancer deaths obser ved compared with the 45.6 deaths expected on the basis of U.S. mortality r ates (standardized mortality ratio [SMR] = 1.69; 95% confidence interval [C I] = 1.3-2.1). Risk increased significantly with increasing number of radio graph exposures cumulative radiation dose. The unadjusted excess relative r isk per Gy was 5.4 (95% CI = 1.2-14.1); when analyses were restricted to pa tients who had undergone at least one radiographic examination, the risk es timate was 2.7 (95% CI = -0.2-9.3). Conclusions. These data suggest that exposure to multiple diagnostic radiog raphic examination during childhood and adolescence may increase the risk o f breast cancer among women with scoliosis; however, potential confounding between radiation dose and severity of disease and thus wit reproductive hi story may explain some of the increased risk observed.