Research

The Sentinel Node Concept

In patients with primary cancer, the tumor status of the lymph nodes is the single most important indicator of outcome. If the first lymph nodes in the drainage pathway to the tumor area contain tumor cells, then the patient probably should receive chemotherapy or hormonal therapy after surgery because the risk of recurrence is high.

The traditional means of determining the tumor status of lymph nodes is lymphadenectomy – surgical removal of some or all of the lymph nodes. The more lymph nodes that are removed, the greater the likelihood that any cancer cells will be found. However, increasing the number of lymph nodes removed also increase the risk of troublesome postoperative complications such as swelling and nerve injury.

Investigators at the John Wayne Cancer Institute (JWCI) have developed a minimally invasive technique that allows surgeons to determine if a primary tumor has spread (“Metastasized”) to nearby lymph nodes. In these 1st studies blue dye is injected into the tissue at the sight of the primary tumor. The blue dye passes along the lymphatic channels that drain this tumor. The first node to turn blue (the “Sentinel node”) is the node most likely to contain any cancer cells migrating from the primary tumor to the drainage basin. Subsequently pre-operative lymphoscintigraphy has been added the morning of or day before surgery. This involves injecting a radiocolloid at the melanoma excision biopsy site and then recording the movement of this tracer in the lymphatic collectors with a gamma camera until the particles reach and are trapped by a lymph node(the sentinel node). This can be marked on the skin and its depth determined to make it easy to find at surgery using a gamma detecting probe. When the surgeon finds the blue "hot" node he knows he has the right one. The surgeon removes this sentinel node (SN) and sends it to the laboratory, where it is examined by a pathologist. If the pathologist finds tumor cells in the node, then all other lymph nodes in the drainage basin are removed. If no tumor cells are found, then no further lymph nodes are removed. Not only is the SN technique much lower in cost than a standard lymphadenectomy, it can be performed with local anesthesia on an outpatient basis with negligible complications.

Dr. Donald L. Morton first proposed the SN concept at the Society of Surgical Oncology Meeting in 1990 for patients with primary cutaneous melanoma. In 1994 Drs. Armando Giuliano and Morton reported on their early experience with SN mapping in patients with breast cancer. Giuliano and Morton showed that SN mapping of the axillary nodes actually improved the ability to detect axillary metastasis when compared to standard axillary dissection. After further refinement of the procedure, in 1997 Dr. Giuliano reported a 94% rate of SN identification in patients with primary breast cancer.

In addition to reducing the risk of complications when compared to traditional lymphadenectomy, the application of the SN mapping concept to patients with cancer increases the pathologist's ability to detect even tiny deposits of tumor in the lymph node. Patients with tumor-positive SNs are usually offered complete lymphadenectomy unless they wish to participate in one of several research trials that are investigating the prognostic impact of nodal disease. Outside of one of these approved multi-institutional research trials, patients with positive SNs are recommended to undergo complete lymphadenectomy at this time.

Results of one of these trials MSLT I have shown an improved disease free survival for patients who are tumor positive in the sentinel node and go on to have a complete node field dissection compared to patients who have a therapeutic dissection of the field only when clinical lymph node metastatases are detected.

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