Sentinel lymph node biopsy in melanoma: pathologic evaluation and diagnostic considerations

Sentinel lymph node biopsy (SLNB) is a widely used staging procedure in melanoma that provides important prognostic information and guides clinical management. The sentinel lymph node (SLN), defined as the first lymph node in the lymphatic drainage pathway from a primary tumor, represents the most likely site of early regional metastasis. Accordingly, identification of metastatic melanoma within SLNs has significant implications for staging and risk stratification and is associated with worse clinical outcomes. The SLNB procedure involves preoperative and intraoperative lymphatic mapping techniques, including radiotracer localization with or without blue dye injection, which allow identification of SLNs. Histopathologic evaluation includes careful gross examination, serial sectioning, and immunohistochemical analysis using melanocytic markers such as SOX10, Melan-A, HMB45, and occasionally PRAME to detect metastatic disease. In addition, prognostic features such as tumor burden, extranodal extension, and microanatomic location of metastases within the lymph node further refine risk assessment. This review provides an overview of SLNB in melanoma, with emphasis on clinical indications, histopathologic evaluation, and key diagnostic and prognostic considerations.