Radiation Therapy and Breast Cancer Risk

Exposure to ionizing radiation has clearly been established as one of the risk factors for the development of breast cancer. Much data on the relationship between radiation exposures and subsequent breast cancer are derived from atomic bomb survivors and women who received medical exposures either for diagnostic or therapeutic purposes. Although these populations differ in background breast cancer risks and the dose, quality, and timing of radiation, consistent findings include an increased risk with younger age at exposure, long latency to breast cancer development, and increasing risk with increasing radiation dose. Although therapeutic radiation is rarely used to treat benign conditions, it remains an important and effective treatment modality for a wide range of cancers. Increased knowledge of radiation-related breast cancer and modifying influences plays an important role in guiding the initial treatment approach for young women and optimizing longterm follow-up care. (JNCCN 2009;7:1121-1128) Female breast cancer is a well-documented late effect of exposure to doses of ionizing radiation as low as 0.1 to 0.5 Sievert (Sv). 1 Sievert is the unit dose equivalent and the product of the absorbed dose in gray and quality factors; in this article, Sv will be used interchangeably with Gray (Gy), the unit of absorbed dose, kerma, and specific energy imparted.