This document discusses the sentinel lymph node concept in early breast cancer. It presents three case studies of patients who underwent segmentectomy or breast-conserving therapy along with sentinel lymph node biopsy for early-stage breast cancer tumors. The sentinel lymph node biopsy procedure involves injecting radioactive tracing agents and blue dye to identify the first draining lymph node from the tumor, which is then biopsied to detect any cancer metastases. The sentinel lymph node biopsy procedure provides accurate assessment of axillary node status while avoiding unnecessary full axillary lymph node dissection for most early-stage breast cancer patients.