The study is a prospective, multi-center, single arm cohort study of omission of adjuvant whole breast radiation therapy (WBRT) following breast conserving surgery (BCS) in patients with a pathological complete response (pCR) following neoadjuvant chemotherapy (NAC). Eligible and consenting female patients with newly diagnosed T1-3 node negative breast cancer with no clinical evidence of distant metastatic disease, who have been treated with NAC, BCS and axillary staging surgery with final pathology demonstrating a pCR (ypT0N0) will be enrolled to the study and followed. The first analysis is planned when follow-up is a median of 5 years. Study participants will not receive adjuvant WBRT, the current standard of care.~The primary outcome is ipsilateral breast tumour recurrence (IBTR) at median 5-year follow-up. Study participants will be followed and assessed for local recurrence, regional recurrence, distant recurrence, DFS and OS. In addition, any additional breast cancer treatments received by the participant for the first recurrence event including repeat BCS, mastectomy, additional systemic therapy and radiation therapy (RT) will be documented. The planned sample size is 352 study participants.
To de-escalate radiation therapy in women with breast cancer.