Diagnosis

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Sentinel Lymph Node (SLN) Biopsy. When Stage I and II melanomas metastasize, they most often spread first to nearby lymph nodes. A procedure called sentinel lymph node (SLN) biopsy helps determine whether lymph nodes might be involved and how far it may have spread. SLN biopsy is now recommended for cancers that are thicker than 1 mm (millimeter) and generally unnecessary for those thinner than 0.75 mm (unless they are ulcerated). Although some evidence suggests this procedure may improve survival, no clinical trials have proven to date that this procedure improves the prognosis in melanoma.

Sentinel node biopsy is a technique which helps determine if a cancer has spread (metastasized), or is contained locally. When a cancer has been detected, often the next step is to find the lymph node closest to the tumor site and retrieve it for analysis. The concept of the "sentinel" node, or the first node to drain the area of the cancer, allows a more accurate staging of the cancer, and leaves unaffected nodes behind to continue the important job of draining fluids. The procedure involves the injection of a dye (sometimes mildly radioactive) to pinpoint the lymph node which is closest to the cancer site. Sentinel node biopsy is used to stage many kinds of cancer, including lung and skin (melanoma).

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This procedure involves the following:

A tiny amount of a tracer, either a radioactively labeled substance (radioisotope) or a blue dye, is injected into the tumor site.
These substances then flow via the lymphatic system into the so-called sentinel node. This is the first lymph node to which any cancer would spread.
The sentinel lymph node and possibly one or two others are then removed and biopsied.

The results of the biopsy can help doctors decide whether to remove other lymph nodes or not. The choices are not always clear cut, however:

If the sentinel node and others shows signs of cancer then the nearby lymph nodes are removed.
If they do not, particularly in Stage I, then it is highly likely that the remainder of the lymph nodes will be cancer free, and further surgery becomes unnecessary.