Pathology of the sentinel lymph node in melanoma

The success and further evolution of the sentinel lymph node (SLN) concept decisively depend on histological techniques. Fundamental standards were agreed on by a panel of international experts from various disciplines in 1999 and published as "The Augsburg Consensus" in 2000. Conventional histology (hematoxylin and eosin [H&E]) has to be supplemented by immunohistochemistry (eg, S100 and HMB45) using adequate series of paraffin sections. Melanoma cells in SLNs must be carefully differentiated from capsular and trabecular nevocytes, from immigrated Langerhans cells, from interdigitating dendritic leukocytes, and from nerve sheath cells, which all share S100 positivity in the cytoplasm. The micromorphometric S classification is based on the maximum distance of intranodal melanoma cells from the interior margin of the SLN capsule. It has proven its practicability under routine circumstances, as well as its predictive value regarding further nodal and distant metastases as well as overall survival. This has to be considered in prospective randomized trials dealing with the issues of completion lymphadenectomy and adjuvant therapies of melanoma patients. Reverse-transcriptase polymerase chain reaction (RT-PCR) techniques, when performed as a supplement to histology on the basis of additional paraffin sections, can further enhance the diagnostic sensitivity for detecting melanoma cells in SLNs.