Breast cancer following irradiation of the breast

During the period 1927--1957 1,115 women were treated at Radiumhemmet, Sweden with ionizing radiation for different non-neoplastic conditions of the breast. The average follow-up period was 31.5 years. The number of breast cancers occurring after irradiation was found to be four times the expected number and the breast cancer incidence rate in the irradiated breasts is dependent on the age of the patient at the first irradiation.