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CancerQuest > Introduction to Patient Information > Introduction to Cancer Detection and Diagnosis > Sentinel Lymph Node Biopsy (SLN) > SLN Biopsy: Methods

SLN Biopsy: Methods

There are two methods used to identify and remove the sentinel node and they differ in the way the sentinel node is located. One method uses an injection of a blue dye and the other uses radioactive material and a gamma counter. The methods are often used in combination, a recent survey by Lucci, et al. polled 410 surgeons in the American College of Surgeons and found that 90% use a combination method of blue dye and radioactive colloid. ⁽¹⁾ The two methods are described in more detail below.

Blue dye

A small amount of blue dye (often isosulfan blue or methylene blue) is injected into the functional elements of the breast (lobules, ducts, etc.). The dye rapidly spreads throughout the region and within 5-10 minutes lymph nodes and vessels can be identified. An angled incision is made in the armpit and the lymphatic vessel marked by the blue dye is located and traced until the lymph nodes are reached. The marked node closest to the tumor is the sentinel lymph node.^{(2) (3)} Allergic reactions have occurred from the injection of the blue dye, but this is very rare (less than 2% of the time) and seldom severe. ⁽⁴⁾

Radioactive Colloid

The radioactive tracer material (sulfur colloid) needs to be injected 4 to 6 hours before surgery for it to properly spread throughout the local lymphatic region. After sufficient time has elapsed, a hand-held gamma ray detector is used to detect increased levels of gamma rays given off by the tracer. The gamma detector will indicate the area of the sentinel node when it shows an increase in count numbers; nodes with high levels of radiation are called "hot nodes". This provides the surgeon the precise location of the sentinel node, preventing the extra tissue disturbance that goes along with the blue dye method. After the sentinel node is removed, the surrounding area is checked for other nodes that are considered hot. Individual surgeon preferences dictate the number of lymph nodes that will be removed. Surgeons typically use one of four criteria to identify sentinel nodes:

• radioactivity greater than 3-4 times than the surrounding area
• radioactivity 10-times higher than a non-sentinel node
• radioactivity 10 times the background count
• radioactivity greater than 25 to 30 per second^{(2) (3)}

References for this page:

1. A Lucci, Jr., PR Kelemen, C Miller III, L Chardkoff, L Wilson. National practice patterns of sentinel lymph node dissection for breast carcinoma. Journal of the American College of Surgeons. 2001; 192: 453-458. [PUBMED]
2. MC Kelley, N Hanson, KM McMasters. Lymphatic mapping and sentinel lymphandectomy for breast cancer. The American Journal of Surgery. 2004; 188: 49-61. [PUBMED]
3. G. PEROS and G.H. SAKORAFAS. Sentinel lymph node biopsy in breast cancer: what a physician should know, a decade after its introduction in clinical practice. European Journal of Cancer. 2007; 16: 318-321. [PUBMED]
4. VM Cimmino, AC Brown, JF Szocik, et al. Allergic reactions to isosulfan blue during sentinel node biopsy-a common event. Surgery. 2001; 130: 439-442. [PUBMED]