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R.E. Mansel et al. (eds.), Metastasis of Breast Cancer, 333-353. © 2007 Springer.

women with early-stage breast cancer are node-negative, and axillary dissection in these women exposes them to the complications of this procedure without any benefit.

The best ideas in clinical medicine are often simple, and the sentinel node concept is of no exception. Sentinel lymph node biopsy is a minimally invasive alternative to axillary lymph node dissection as a way of staging breast cancer in clinically node-negative patients. A sentinel lymph node is defined as any lymph node that receives direct lymphatic drainage from a primary tumour site (Figure 1). Therefore, if the sentinel lymph node (SLN) is not involved with metastatic disease, the remainder of the lymph nodes should also be negative. Likewise, if the SLN is positive, there is a risk that higher order nodes may be involved with metastatic disease.

Figure 1. Sentinel lymph node (SLN) receives direct lymph drainage from the primary tumour.

Cabanas (6) introduced the concept of "sentinel node" in 1977 when he used lymphangiograms performed via dorsal lymphatics of the penis to demonstrate the existence of a specific node or group of nodes associated with the superficial epigastric vein that predicted the nodal status of penile carcinoma. In 1992, Morton et al. (7) described lymphatic mapping utilising an intradermal isosulfan blue dye injection technique for malignant melanoma and were the first to employ this concept to localise SLNs in patients with malignant melanoma. The authors demonstrated a high success rate in both identifying a SLN (82%) and in achieving low false-negative rate (1%). In 1993, Alex and Krag (8) introduced the use of a radioactive tracer 99mTechnetium sulphur colloid injected intradermally around a primary melanoma site, followed by imaging and subsequent intraoperative use of a gamma probe to localise and extirpate the SLN. Krag et al. (9) then applied radiolocalisation to the staging of breast cancer. Giuliano et al. (10) in 1994 modified Morton's technique of intraoperative lymphatic mapping using blue dye and applied it to breast cancer. Giuliano injected isosulfan blue dye into the breast tumour and the surrounding parenchyma in 174 patients. An incision was made in the axilla and all blue lymphatic channels were identified and traced to a blue node (Figure 2). A sensitivity of 88% and a false-negative rate of 6.5% were found. Subsequently, large studies have shown that using both blue dye and radioisotope together improves the SLN detection rate (percentage of patients in whom a sentinel lymph node is found) and reduces the false-negative rate (number of patients with a negative sentinel lymph node who actually have undetected axillary nodal metastases).

Figure 2. Blue-stained lymphatic leading to a blue sentinel lymph node.

Sentinel lymph node biopsy (SLNB) appears to reliably identify node-negative patients who can be spared the morbidity resulting from axillary lymph node dissection. Non-randomised studies of sentinel node biopsy followed by axillary lymph node dissection have demonstrated that one or more SLNs can be identified in more than 90% of patients with invasive breast cancer, with a false-negative rate of 10% or less (9, 11, 12).

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