Sentinel node biopsy: not only a staging tool?

The management of clinically negative regional lymph nodes in early-stage melanoma has been controversial for at least a century. While some surgeons offer elective lymph node dissection (ELND), others recommend treatment of the primary alone and only perform a therapeutic dissection (TLND) for cases of recurrence in the nodal basin. The rationale for ELND is based on the concept that metastases occur via the sequential passage of tumor from the primary site to the regional lymph nodes and then to more distant sites. If this theory is correct then early dissection of the regional lymph nodes will disrupt the metastatic cascade and prevent further spread of disease. On the other hand, advocates of the "wait and watch" approach suggest that metastases to the regional lymph node basin are only a marker of disease progression and that distant disease can occur in the absence of lymph node metastases. Four randomized prospective studies have examined the efficacy of ELND versus TLND. While all four studies have failed to demonstrate a survival advantage of ELND, there is some suggestion that patients with metastases in the regional basin may benefit from ELND. As an alternative approach to this controversy, Morton and associates at the John Wayne Cancer Institute devised the technique of intraoperative lymphatic mapping and sentinel lymphadenectomy (LM/SL). This minimally invasive operative procedure allows the surgeon to identify the first or sentinel lymph (SN) in the regional basin. The technique is predicated on accurate mapping of the cutaneous lymphatics by lymphoscintigraphy and the intraoperative use of a vital blue dye to lead the surgeon to the SN and allow the pathologists to identify metastases in the lymph nodes. Patients with tumor-positive dissections would undergo complete lymph node dissection (CLND), and for those without metastases the complications and costs associated with CLND could be avoided. The success of the procedure depends on the completion of a learning phase and on the cooperation of nuclear medicine physicians, surgeons, and pathologists. While this technique has become almost standard practice in the United States and around the world, we await the results of several important clinical trials to determine whether LM/SL will replace ELND or the wait and watch approach in the management of early-stage melanoma.