Breast cancer patients often receive systemic drugs as the initial curative treatment of their disease. The initial systemic therapy leads to a variable degree of tumor shrinkage. At present, there is no evidence-based consensus among breast surgeons on the optimal extent of resection after considerable tumor shrinkage and whether resection margin should be designed according to the tumor extent before treatment or the extent after treatment. This trial will help determine the optimal extent of resection in tumors that exhibits a significant change in volume after primary systemic therapy.

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?

Inclusion Criteria:

• Biopsy-proven diagnosis of invasive adenocarcinoma of the breast.
• Tumor stage T 1-4b
• Nodal stage N 0-2
• ASA (American Society of Anesthesiologists) class I-II

Exclusion Criteria:

• Patients opting for mastectomy.
• Patients advised for mastectomy by the treating physician.
• Patients opting for primary surgical treatment.
• Patients advised for primary surgical treatment by the treating physician.
• Metastatic patients.
• Multifocal tumors.
• Lobular neoplasia.
• Current pregnancy or pregnancy less than 6 months from the enrollment date.
• Active second cancer.