The sentinel lymph node is the hypothetical first lymph node or group of nodes draining a cancer. In case of established cancerous dissemination it is postulated that the sentinel lymph nodes are the target organs primarily reached by metastasizing cancer cells from the tumor. The sentinel node procedure (also termed sentinel lymph node biopsy or SLNB) is the identification, removal and analysis of the sentinel lymph nodes of a particular tumour. Physiology The spread of some forms of cancer usually follows an orderly progression, spreading first to regional lymph nodes, then the next echelon of lymph nodes, and so on, since the flow of lymph is directional, meaning that some cancers spread in a predictable fashion from where the cancer started. In these cases, if the cancer spreads it will spread first to lymph nodes (lymph glands) close to the tumor before it spreads to other parts of the body. The concept of sentinel lymph node surgery is to determine if the cancer has spread to the very first draining lymph node (called the "sentinel lymph node") or not. If the sentinel lymph node does not contain cancer, then there is a high likelihood that the cancer has not spread to any other area of the body. Uses The concept of the sentinel lymph node is important because of the advent of the sentinel lymph node biopsy technique, also known as a sentinel node procedure. This technique is used in the staging of certain types of cancer to see if they have spread to any lymph nodes, since lymph node metastasis is one of the most important prognostic signs. It can also guide the surgeon to the appropriate therapy. There are various procedures entailing the sentinel node detection: Preoperative planar lymphoscintigraphy Preoperative planar lymphoscintigraphy in conjunction with SPECT/CT [single photonemission CT (SPECT) with a low-dose CT] Intraoperative visual blue dye detection Intraoperative fluorescence detection (fluorescence image-guided surgery) Intraoperative gamma probe/Geiger meter-detection Preoperative or intraoperative super paramagnetic iron oxide nanoparticles injection, detection by using Sentimag instrument Postoperative scintigraphy of main specimen with planar acquisition In everyday clinical activity, entailing sentinel node detection and sentinel lymph node biopsy, it is not required to include all different techniques listed above. In skilled hands and in a center with sound routines, one, two or three of the listed methods can be considered sufficient. To perform a sentinel lymph node biopsy, the physician performs a