Spitz nevus and atypical spitzoid neoplasm.

Spitz nevus (SN) and Spitzoid malignant melanoma (SMM) represent benign and malignant counterparts at both ends of the spectrum of Spitzoid lesions. Atypical Spitzoid neoplasm (ASN) is a poorly defined and characterized category of melanocytic tumors with histologic features of both benign Spitz nevi and malignant melanomas. The group of ASN represents a mixture of Spitz nevi with atypical features and Spitzoid melanomas. However, at the current moment in time, histopathologists are not capable of differentiating between the 2 in some cases and are forced to place them in this ambiguous category, where the behavior of these lesions cannot be predicted with certainty. Because this group encompasses both benign and malignant lesions, and perhaps also a separate category of melanocytic tumors that behave better than conventional melanomas, some of these neoplasms can metastasize and kill patients, whereas others have no metastatic potential, and yet others might only metastasize to regional lymph nodes. Although diagnostic accuracy has improved over the years, many of these lesions remain controversial, and there is still poor interobserver agreement in classifying problematic Spitzoid lesions among experienced dermatopathologists. The objective of this review article is to summarize the most relevant information about SN and ASNs. At this time histologic examination remains the golden standard for diagnosing these melanocytic neoplasms. We therefore concentrate on the histopathologic, clinical, and dermoscopic aspects of these lesions. We also review the most recent advances in immunohistochemical and molecular diagnostics as well as discuss the controversies and dilemma regarding whether to consider sentinel lymph node biopsy for diagnostically ambiguous melanocytic neoplasms.