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



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.


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.[1]

A blue stained sentinel lymph node in the axilla.
A micrograph showing an adenocarcinoma of the breast (dark pink) in a lymph node (purple) and extending into the surrounding fat (white, chicken-wire appearance). H&E stain.

To perform a sentinel lymph node biopsy, the physician performs a lymphoscintigraphy, wherein a harmless radioactive substance is injected near the tumor. The injected substance, Filtered Sulfur Colloid, is tagged with the radionuclide Technetium-99m. The injection protocols differ by doctor but the most common is a 500 μCi dose divided among 5 tuberculin syringes with 1/2 inch, 24 gauge needles. The sulphur colloid is slightly acidic and causes minor stinging. A gentle massage of the injection sites spreads the sulphur colloid, relieving the pain and speeding up the lymph uptake. Scintigraphic imaging is usually started within 5 minutes of injection and the node appears from 5 min to 1 hour. This is usually done several hours before the actual biopsy. About 15 minutes before the biopsy the physician injects a blue dye in the same manner. Then, during the biopsy, the physician visually inspects the lymph nodes for staining and uses a Gamma Probe or 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 surgeon 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 takes less than 20 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.[2]


However, the technique is not without drawbacks, particularly when used for melanoma patients. This technique only has therapeutic value in patients with positive nodes.[3] Failure to detect cancer cells in the sentinel node can lead to a false negative result - there may still be cancerous cells in the lymph node basin. In addition, there is no compelling evidence that patients who have a full lymph node dissection as a result of a positive sentinel lymph node result have improved survival compared to those who do not have a full dissection until later in their disease, when the lymph nodes can be felt by a physician. Such patients may be having an unnecessary full dissection, with the attendant risk of lymphedema.[4]


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.[5]


  1. ^ Robbins and Cotran, Pathological Basis of Disease 8th edition pp. 270
  2. ^ Tanis PJ, Boom RP, Koops HS, Faneyte IF, Peterse JL, Nieweg OE, Rutgers EJ, Tiebosch AT, Kroon BB (2001a). Frozen section investigation of the sentinel node in malignant melanoma and breast cancer. Ann Surg Oncol 8:222-6. PMID 11314938.
  3. ^ Wagman LD. "Principles of Surgical Oncology" in Pazdur R, Wagman LD, Camphausen KA, Hoskins WJ (Eds) Cancer Management: A Multidisciplinary Approach. 11 ed. 2008.
  4. ^ Thomas J (2008). Prognostic false-positivity of the sentinel node in melanoma. Nat Clin Pract Oncol. 5(1):18-23. PMID 18097453.
  5. ^ Tanis PJ, Nieweg OE, Valdes Olmos RA, Th Rutgers EJ, Kroon BB (2001b). History of sentinel node and validation of the technique. Breast Cancer Res 3:109-12. PMID 11250756.

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