Partial Breast Versus no Irradiation for Women With Early Breast Cancer

International standard of therapy is to provide adjuvant breast radiation therapy (RT) after breast conserving surgery for an early breast cancer to lower the risk of local and distant failures. However, breast cancer is a heterogeneous disease, and the gain from RT in selected low risk patients is low. RT may cause acute and late side effects, and some of these may be serious to the patient. Therefore, there is a need to tailor RT utilization to the individual recurrence risk and try identify patients who are unlikely to gain much risk reduction from RT, because those patients can then omit RT and thereby avoid late effects and over‐treatment. At the present time there is no consensus as to define the selection criteria for patients who may omit RT. Based on early results from the randomized DBCG RT PBI trial, external beam 40 Gy/15 fr partial breast irradiation (PBI) has been standard in Denmark since April 2016 for selected low risk breast cancer patients. Based on results from the UK IMPORT LOW trial, the 5 yr local recurrence risk using this technique for PBI is 0.5%, whilst 2% for developing a new contralateral breast cancer. This trial will investigate if PBI can safely be omitted in selected low risk breast cancer patients without causing unacceptable high risk of local failure.