Radioguided sentinel lymph node biopsy in malignant cutaneous melanoma

Abstract

The procedure of sentinel lymph node biopsy in patients with malignant cutaneous melanoma has evolved from the notion that the tumor drains in a logical way through the lymphatic system, from the first to subsequent levels. As a consequence, the first lymph node encountered (the sentinel node) will most likely be the first affected by metastasis; therefore, a negative sentinel node makes it highly unlikely that other nodes in the same lymphatic basin are affected. Although the long-term therapeutic benefit of the sentinel lymph node biopsy per se has not yet been ascertained, this procedure distinguishes patients without nodal metastases, who can avoid nodal basin dissection with its associated risk of lymphedema, from those with metastatic involvement, who may benefit from additional therapy. Sentinel lymph node biopsy would represent a significant advantage as a minimally invasive procedure, considering that an average of only 20% of melanoma patients with a Breslow thickness between 1.5 and 4 mm harbor metastasis in their sentinel node and are therefore candidates for elective lymph node dissection. Furthermore, histologic sampling errors (amounting to approximately 12% of lymph nodes in the conventional routine) can be reduced if one assesses a single (sentinel) node extensively rather than assessing the standard few histologic sections in a high number of lymph nodes per patient. The cells from which cutaneous melanomas originate are located between the dermis and the epidermis, a zone that drains to the inner lymphatic network in the reticular dermis and, in turn, to larger collecting lymphatics in the subcutis. Therefore, the optimal route for interstitial administration of radiocolloids for lymphoscintigraphy and subsequent radioguided sentinel lymph node biopsy is intradermal or subdermal injection. (99m)Tc-Labeled colloids in various size ranges are equally adequate for radioguided sentinel lymph node biopsy in patients with cutaneous melanoma, depending on local experience and availability. For melanomas along the midline of the head, neck, and trunk, particular consideration should be given to ambiguous lymphatic drainage, which frequently requires interstitial administration virtually all around the tumor or surgical scar from prior excision of the melanoma. Lymphoscintigraphy is an essential part of radioguided sentinel lymph node biopsy because images are used to direct the surgeon to the sites of the nodes. The sentinel lymph node should have a significantly higher count than that of the background (at least 10:1 intraoperatively). After removal of the sentinel node, the surgical bed must be reexamined to ensure that all radioactive sites are identified and removed for analysis. Virtually the entire sentinel lymph node should be processed for histopathology, including both conventional hematoxylin-eosin staining and immune staining with antibodies to the S-100 and HMB-45 antigens. The success rate of radioguidance in localizing the sentinel lymph node in melanoma patients is approximately 98% in institutions that perform a high number of procedures and approaches 99% when combined with the vital blue-dye technique. Growing evidence of the high correlation between a sentinel lymph node biopsy negative for cancer and a negative status for the lymphatic basin-evidence, therefore, of the high prognostic value of sentinel node biopsy-has led to the procedure's being included in the most recent version of the TNM staging system and starting to become the standard of care for patients with cutaneous melanoma.