A great deal of clinical experience has firmly established the concept of the sentinel lymph node (SN) in breast cancer. SN biopsy allows treatment without axillary lymphadenectomy and has made it possible to perform a surgical intervention via just a small skin incision. In partial resection of the breast (quadrantectomy), we use a double retractor to form a workspace under the skin via a small axillary incision. Resection does not require a large incision even in cases in which the cancer lesion is located in the upper inner or lower inner quadrant of the breast, as the endoscope allows the surgeon to see the workspace formed by the double retractors.