Three Types of Nodal Melanocytic Nevi in Sentinel Lymph Nodes of Patients With Melanoma: Pitfalls, Immunohistochemistry, and a Review of the Literature.

The presence or absence of metastasis in sentinel lymph nodes often drives melanoma staging, prognosis, and treatment. However, distinguishing between metastatic melanoma cells and clusters of benign melanocytic nevus cells is not always straightforward. When morphologic hematoxylin and eosin interpretation alone is not sufficient, additional hematoxylin and eosin sections and immunohistochemical (IHC) studies may be beneficial. This review and small cases series of 3 diagnostically challenging melanocytic sentinel lymph node cases highlights the IHC approach to evaluate intraparenchymal nodal melanocytic nevi, coexistent metastatic melanoma with adjacent melanocytic nevi cells, and nodal blue nevi. In challenging cases, cytological morphology of the melanocytes, location within the lymph node, and IHC studies may assist in diagnosis. If these tools yield conflicting results, expert opinion is recommended.