Primary systemic (neoadjuvant) therapy (NAT) is a widely practised curative treatment for invasive breast cancer. Neoadjuvant chemotherapy (before surgery) and adjuvant chemotherapy (after surgery) had equivalent survival rates in major randomized trials. In these studies, preoperative systemic therapy increased the patient's chance to achieve breast conservation. The down side was a clear trend towards increased ipsilateral breast tumor recurrence. Preoperative chemotherapy leads to patchy, irregular cell death known as honeycomb effect and thus may lead to a misleading false negative resection margin of a tumorectomy operation. Even with the advent of oncoplastic techniques which allowed larger resection volumes with satisfactory cosmetic results, rates of re-excision, mastectomy and local relapse did not differ from those after traditional lumpectomy operations. As of today, there is no consensus -based on evidence- on the optimal width of margin in patients who are offered breast conservative surgery (BCS) after systemic therapy. In view of the current uncertainty and lack of evidence, The present trial is designed to answer the following question (Specific aim): Does planning the resection margin according to the pre-treatment tumor extent improve the local recurrence rate in patients receiving breast conservative surgery after systemic therapy?
