Sentinel lymph node

Overview
The sentinel lymph node is the hypothetical first lymph node or group of nodes reached by metastasizing cancer cells from a tumor.

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 unidirectional.

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.

To perform a sentinel lymph node biopsy, the physician performs a lymphoscintigraphy, wherein he first injects blue dye and a harmless radioactive substance near the tumor. This is usually done several hours before the actual biopsy. Then, during the biopsy, the physician visually inspects the lymph nodes for staining and uses a Geiger counter to assess which lymph nodes have taken up the radionuclide. One or several nodes may take up the dye and radioactive tracer, and these nodes are designated the sentinel lymph nodes. The physician then removes these lymph nodes and sends them to a pathologist for rapid examination under a microscope to look for the presence of cancer. A frozen section procedure is commonly employed (which lasts 20-30 minutes), so if neoplasia is detected in the lymph node a further lymph node dissection may be performed. With malignant melanoma, many pathologists eschew frozen sections for more accurate "permanent" specimen preparation due to the increased instances of false-negative with melanocytic staining.

There are various advantages to the sentinel node procedure. First and foremost, it decreases unnecessary lymph node dissections where this is not necessary, thereby reducing the risk of lymphedema, a common complication of this procedure. Increased attention on the node(s) identified to most likely contain metastasis is also more likely to detect micro-metastasis and result in staging and treatment changes. The main uses are in breast cancer and malignant melanoma surgery, although it has been used in other tumor types (colon cancer) with a degree of success (Tanis et al 2001a).

The sentinel node procedure in breast cancer was pioneered by surgical oncologist, Armando Giuliano, MD at the John Wayne Cancer Institute in the 1990s, and confirmative trials followed soon after (Tanis et al 2001b).