Introduction to the Sentinel Lymph Node as a Gatekeeper of Cancer Spread Concept

The first lymph node to receive drainage from a primary tumor is called a sentinel lymph node, acting as a “gatekeeper” for metastatic spread. Surgical techniques have been developed to visualize and biopsy the sentinel lymph node by injecting dyes into the primary tumor to map out the lymphatic flow. The subsequent pathological examination of the resected sentinel lymph nodes can help determine the extent of a cancerous metastatic spread and provide valuable information regarding prognosis and clinical management for patients with various malignancies, including melanoma, breast cancer, gynecologic cancers, and head and neck cancers. Importantly, since these procedures are less invasive than surgical dissections, sentinel lymph node evaluation can reduce the morbidity associated with complete surgical lymph node dissection. The purpose of this chapter is to introduce the concept of the sentinel lymph node and its role in lymphatic medicine, with a focus on its clinical applications across several types of cancer.