Tagging the Node

Translating the discovery of the sentinel node to clinical practice required a sure way to "tag" the sentinel node, so the surgeon could distinguish it unfailingly from the many lymph nodes surrounding it.

Elissa Kramer, MD, Associate Professor of Clinical Radiology at NYU, outlines the "tagging" process:

Three methods of identification are used at NYU to guarantee accurate detection of the sentinel node. First, several days before sugery, lymphoscintigraphy is used to map the lymph flow into the sentinel node and mark the skin above it. Second, just prior to surgery, a radioisotope is injected into the melanoma site. The radioactive isotope drains into the sentinel node, so that a gamma probe (a hand-held sensor attached to a geiger counter) can detect the node's location. Third, a blue dye is injected into the site of the melanoma which is carried by the lymphatics directly to the sentinel node. The arrival of this dye stains the sentinel node blue Ñ which makes it clearly visible to the surgeon. Dr. Roses credits Dr. Donald Morton, MD, Director of the John Wayne Cancer Institute, with the development of this technique. Dr. Roses is a principal investigator on a multicenter study of this sentinel node procedure, supported by the National Cancer Institute and directed by Dr. Morton.

Finding the Node

After the melanoma site is injected with both radioisotope and blue dye, an incision is made in the skin above the sentinel node, identified by lymphoscintigraphy. The surgeon then inserts the gamma probe to detect radioactivity in the draining node, and identifies the "hot" sentinel node, which has the highest level of radioactivity. Next, the surgeon confirms that this is in fact the sentinel node by its blue color and removes it.

Analysis by the Pathologist

With the patient still in surgery, pathologists immediately begin an exacting and sophisticated microscopic examination of the sentinel node to search for any malignant cells. While waiting for the pathologic evaluation, the surgeon performs a wide and deep excision at the melanoma site. If the pathologist finds metastasis in the sentinel node, a complete lymphadenectomy is performed. In 3 out of 4 cases no metastasis is found and the patient goes home without further surgery.

"Analysis of the sentinel node for the presence of melanoma doesn't stop there. The lab processes and analyzes a series of slides for several days following surgery. Specialized immunological staining and other precise techniques enable the pathologist to detect tumor deposits consisting of as few as 5 to 10 malignant cells in the entire node — and achieve remarkable diagnostic accuracy."
— pathologist Johnathan Melamed, MD