Faye Lim, Grace Kusumawidjaja Assessing the effect and outcome of axillary radiotherapy in patients with cN0 disease who are then yN0 but have evidence of treatment effect in the nodes post neoadjuvant chemotherapy on sentinel lymph node biopsy Abstract Disclosures Abstract: Little evidence is available to guide decision making to offer axillary radiotherapy to ladies who present initially with clinically node negative disease but then show evidence of treatment effect /scarring in the lymph nodes post neoadjuvant chemotherapy. Often surgery is a sentinel lymph node biopsy or sampling and not a formal dissection. The decision to give axillary radiotherapy is based on a multitude of factors including response post neoadjuvant chemotherapy, the initial grade of the cancer, the presence of lymphovascular invasion and the hormone receptor status / HER2 status. This study aims to 1. Look at this Radiotherapy decision making process in detail 2. Determine the effect of giving axillary radiotherapy on relapse rate and survival 3. Determine the toxicity from giving axillary radiotherapy Joint Breast Cancer Registry Singapore