Sentinel node in melanoma

Abstract

Sentinel node (SN) biopsy in melanoma was not only the first modern clinical application of this procedure in oncology but it also constituted the first groundbreaking evidence for the actualized SN concept. Regional lymph nodes are usually the first site of melanoma metastasis preceding systemic spreading of the disease; therefore, reliable assessment of involvement in the lymph node basins where the primary cutaneous melanoma lesion drains is of vital importance. Originally validated for melanoma lesions with intermediate Breslow thickness (1–4mm) currently SN biopsy is also recommended for lesions from 0.8 to1 mm thickness with presence of ulceration. The procedure can also be considered for thicker melanomas (>4mm). In the operating room guidance was originally based on blue dye mapping, chronologically almost immediately followed by the incorporation of radioguided surgery using intracutaneous radiocolloid injections around the primary lesion or the excision scar. The possibility to generate lymphatic drainage imaging previous to the surgical act with the same radiotracer transformed the use of radioguidance in standard of care for performing SN biopsy in melanoma. From the beginning preoperative lymphatic mapping has been based on lymphoscintigraphy which is a sequential study with a dynamic part, acquired immediately after radiotracer administration, as well as early and delayed planar static images. In this millennium the integration of SPECT/CT in standard gamma cameras led to incorporate this modality to the SN procedure providing essential anatomical information to surgically localize SNs. With SPECT/CT the SN location can be related to specific landmarks such as blood vessels, muscles and other structures. Initial multicenter studies confirmed the accuracy and reliability of SN biopsy for regional lymph node staging with the SN status as the single most important prognostic factor in clinically negative melanoma patients. Recent trials have showed no melanoma specific survival benefits between immediate regional lymphadenectomy and active ultrasound surveillance in the case of metastatic SNs. In this context, SN lymphatic mapping has become crucial to assess which lymph node basins at risk need to be controlled during follow-up.