 the development of new drugs and improved understanding of tumor biology have significantly altered the management of breast cancer. Radical mastectomies, which had been the primary treatment for breast cancer for over a century, were based on the assumption that breast cancer was a local regional disease. Studies conducted in the 1970s showed that cancer cells could spread to the systemic circulation without passing through the regional lymphatic system, leading to multidisciplinary treatment of breast cancer. This included breast conserving surgery, BSC+, combined with axillary dissection, AD, systemic chemotherapy, hormonal therapy, and radiation therapy in early stage breast cancer. Later clinical trials demonstrated that the breast could be preserved in those who responded well to neo-adjuvant chemotherapy, NAC. In the early 1990s, sentinel lymph node biopsy, SLNB, was used to identify patients with early stage breast cancer, CN0, who would benefit from axillary dissection. This procedure was found to avoid the serious complication of lymphedema while still providing accurate staging information.