The current standard of care for patients with early breast cancer is radiation therapy (RT) after breast conserving surgery to improve cancer control. However, breast cancer is a complex disease, and the benefit of radiation therapy in individual patients varies. Therefore, delivery of radiation therapy in all patients may lead to over-treatment of some of them, potentially resulting in unnecessary treatment toxicity, financial costs and logistical challenges for these patients. However, clinical trials have not consistently identified patients who may safely omit radiation using conventional clinical and pathological characteristics. EXPERT is an investigator initiated clinical trial which presents a unique opportunity to improve personalised use of radiation therapy in patients with early breast cancer according to their individual risks of local recurrence. The primary aim of the trial is to see whether a genomic test of breast cancer tissue can be used to identify women who can safely avoid radiation therapy after breast cancer surgery. The need for radiation therapy after breast cancer surgery depends on the risk of the cancer coming back. If the doctor could identify women who have a very small risk of the cancer coming back, these women may not need radiation therapy and could avoid its side effects.