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This report presents data on the long-term risks of developing malignancies other than breast cancer after exposure to scattered doses of ionizing radiation. The estimates were based on a cohort of 3,090 women who were diagnosed clinically with benign breast disease between 1925 and 1961. A total of 1,216 women were treated with radiation therapy. The breasts received a mean absorbed dose of 5.84 Gy. Mean absorbed doses owing to scatter to 14 other organs were also determined. The lung received the highest mean scattered dose (0.75 Gy; range 0.004-8.98 Gy) and rectum the lowest (0.008 Gy; range 0-0.06 Gy). Median age at first exposure was 40 years. The follow-up lasted up to 61 years after treatment (mean follow-up 27 years). End-point data were obtained from population-based registers. With internal reference the relative risk for non-breast solid tumors was 1.2 (95% confidence interval 1.0-1.5). However, this excess was not apparent when comparison with the general population was made (standardized incidence ratio = 0.95; 95% confidence interval 0.84-1.07). Among individual sites no significantly increased risks were observed. For stomach cancer there was a linear increase with dose (ERR/Gy = 1.3; two-sided P = 0.05). No increased risk was observed for leukemias. In two earlier reports, breast cancer incidence has been shown to be significantly increased in this cohort of irradiated women. Our results suggest that the scattered doses from the breast irradiation may have increased the risk of cancers of other sites, but the small number of cases in different locations precludes strong interpretations.

Exposure of the breast to ionising radiation increases the risk of breast cancer, especially among young women. However, some issues remain controversial, for instance the shape of the dose-response curve and the expression of time-related excess. The main purpose of this report was to examine the dose-response curves for radiation-induced breast cancer formulated according to radiobiological target theories. Another purpose was to analyse the time-related excess of breast cancer risk after exposure when dose and age at first exposure were held constant. Breast cancer incidence was analysed in a cohort of 3090 women diagnosed with benign breast disease during 1925-61 (median age 37 years). Of these, 1216 were treated with radiation therapy. The dose range was 0-50 Gy (mean 5.8 Gy). The incidence rate as function of dose was analysed using a linear-quadratic Poisson regression model. Cell-killing effects and other modifying effects were incorporated through additional log-linear terms. Additive and multiplicative models were compared in estimating the time-related excess. The analysis, which was based on 278 breast cancer cases, showed a linear dose-response relationship at low to medium dose levels with a cell-killing effect of 5% Gy-1 (95% confidence interval 2-9%). For a given absorbed dose and age at first exposure the time-related excess was proportional to the background rates with a suggestion that the excess remains throughout life.

Background: From the 1920s through the 1950s, radiation therapy was used in Sweden as a treatment for benign breast diseases. It is now known that exposure of the breast to ionizing radiation increases the relative risk of subsequent breast cancer, especially for younger women. However, the degree to which the patient's age contributes to the elevation of risk for subsequent development of breast cancer is not yet completely understood., Purpose: The purpose was to study the risk of breast cancer after irradiation of the female breast and, in particular, to analyze the duration of the effect and the risk for women older than 40 years at first exposure., Methods: In this cohort study, data were obtained through population-based registers. The exposed group consisted of 1216 women (median age, 40 years) who, during the period spanning 1925 through 1954, received radiation therapy for benign breast disease. The reference group consisted of 1874 women (median age, 36 years) who had the same diagnosis during that time period but did not receive radiation therapy. The radiation doses were determined from the original medical records (mean dose, 5.8 Gy; range, 0.003-50.1 Gy). The follow-up lasted up to 60 years after first exposure. The incidence rate ratio was analyzed with Poisson regression models., Results: The total number of breast cancers in the exposed cohort was 198 versus 101 in the unexposed cohort. Overall, the radiation-associated incidence rate ratio was 3.58 (95% confidence interval = 2.77-4.63). The dose-response gradient was statistically significant (P < .001) but leveled off at higher doses. The incidence rate ratios decreased starting about 25 years after first exposure but were at increased levels throughout the entire follow-up period. The incidence rate ratio decreased with age at first exposure but was significantly increased (P < .001) even when the age at time of first exposure was greater than 40 years., Conclusions: Total dose, age at first exposure, and time since first exposure were all determinants of the incidence rate ratio of breast cancer after exposure of the breast to ionizing radiation. A statistically significant increase in the incidence of breast cancer following radiation treatment of various benign breast diseases was observed even among women older than 40 years at the time of first treatment., Implications: These findings need to be considered when weighing the relative benefits versus risks of generalized screening of younger women for breast cancer by mammography.

A case-control study of Swedish thyroid cancer patients was conducted to evaluate the possible influence of 131I treatment and external radiotherapy on the risk of developing a subsequent cancer. Both cases and controls derived from a cohort of Swedish thyroid cancer patients treated with 131I (n = 834) or by other means (n = 1,121). Thirty-six breast, 13 stomach, 12 kidney, and 5 bladder cancers were found more than 2 years after 131I treatment/thyroid cancer diagnosis. Individual, absorbed dose in the organs was calculated by using ICRP tables, administered activity of 131I, and 24-h 131I uptake. In studying the effect of 131I and external radiotherapy no statistically significant dose-response relationships were found for cancers of the breast, stomach, bladder or kidney. When the absorbed dose from 131I was analyzed separately the risks remained essentially the same. The present follow-up time and the relatively low absorbed dose that the patients received from 131I and external radiotherapy necessitate studies with a longer follow-up time or a larger patient material before more firm conclusions can be made.