The most significant prognostic factor in most solid tumors is regional lymph node status. Patients with nodal metastasis in melanoma have a 40% decrease in 5 year survival as compared to node negative patients. Evaluation of nodal basins in melanoma has evolved in recent years with the advent of sentinel node biopsy techniques. First described by Morton et al, the sentinel lymph node (SLN) is the first node in a regional basin that receives cutaneous lymphatic afferents from a primary tumor. It is believed the sentinel node, whether positive or negative for tumor, can accurately predict the status of the remaining nodes.

One important factor in determining the status of the nodes is the method of pathologic evaluation. Standard pathologic evaluation takes one to two sections from the center of the node with routine H&E staining and histologic evaluation. This studies less than 1% of the total nodal tissue. Other studies have shown that routine histologic evaluation of regional nodes can fail to detect as high as 50% of meta-static disease. This suggests the presence of micrometastatic disease that was missed by routine histopathology. With SLNB, one or two nodes most likely to contain metastasis are submitted for evaluation. This allows for a more detailed examination of the tissue with serial sectioning, immunohistochemical staining and molecular staging techniques. However, specimens from a completion lymph node dissection are typically examined with standard histopathology and may miss micrometastatic disease.

Intradermal Injection Radiocolloid

Blue Dye Peritumoraly Intraoperative^

Gamma Probe Localization

Identification of Blue and/or Hot SLN

Figure 8.1. Sentinel node biopsy technique.

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