Breast cancer is a public health problem in both developed and developing countries. 1-3 According to the International Agency for Research on Cancer (IARC), there were two million new cancer cases and 626,000 deaths from breast cancer worldwide in 2018. 1 In Brazil, breast cancer accounts for about 30% of all new cancer cases in women, annually. 2 In this context, studies on risk factors are important for understanding the problem and for developing disease prevention policies. Exposure to ionizing radiation is a well-known risk factor for the development of breast cancer. The risk is highest among young women at the time of exposure and is directly proportional to the radiation dose. 4 In this context, there are several associations with genetic factors, which suggest that certain variations in deoxyribonucleic acid (DNA) damage-response genes can make it difficult for radiation-induced damage to be repaired. 5 On the other hand, little is known about the impact of major radiological accidents on breast cancer incidence. The data from Japan and Chernobyl remain inconclusive, despite the increased risk of several other pathological conditions. 4,6 In September 1987, a radiological accident of major proportions occurred in Goiânia, which affected both the population and the environment. The accident was caused by the removal and dismantling of a sealed source containing cesium-137, in an abandoned radiotherapy unit in Goiânia. 7,8 The source was in the form of cesium chloride salt, which exhibited high solubility and was easily dispersible. The weather conditions at the time of the accident comprised heavy rain and a temperature of 26.4 °C. These conditions facilitated dispersion of the initial cesium-137 in the environment, around seven main spots in the central region of the city of Goiânia.