Atypical Spitz Tumor of Uncertain Biologic Potential with Inopportune Localization in a 7-year-old Boy.

The Spitz nevus was first described as the “melanoma of childhood” or “juvenile melanoma” by Sophie Spitz in 1948 (1). Most spitzoid melanocytic proliferations can be classified as benign Spitz nevi or spitzoid melanomas based on published criteria (2-3). However, a subset of spitzoid lesions have histological features that deviate from a typical Spitz nevus, yet are insufficient for a definitive diagnosis of spitzoid melanoma. The scope of spitzoid melanocytic proliferations includes the typical Spitz nevus, dysplastic Spitz nevus, Spitz nevus with atypia, melanoma evolving into a Spitz nevus, and spitzoid melanoma arising de novo (4). Lack of uniform criteria for discrimination between malignant and benign spitzoid melanocytic lesions makes it very difficult for pathologists and clinicians to interpret the histopathological findings and give an unequivocal diagnosis of melanoma. Using only histopathological criteria, it is often very difficult to differentiate melanoma arising in a Spitz nevus from a Spitz nevus with severe atypia. Thus, the term Spitz tumor of uncertain malignant potential (STUMP) is often used (5). Molecular methods have been employed recently to evaluate a spectrum of melanocytic lesions, including Spitz nevi. Molecular methods used for discrimination between malignant and benign spitzoid tumors include fluorescence in situ hybridization (FISH) and sequencing. The FISH method employs hybridization of specific fluorescent probes to gene regions and/or chromosomes. If there are more or less chromosome/gene copies than two per cell, it is regarded as an abnormality. Sequencing methods compare the genetic code of bioptic samples to the reference gene sequence found online and discrepancies, mutations, insertions, or deletions of the analyzed gene are noted. While there have been some indications of a higher rate of chromosomal abnormalities and pathogenic mutations in spitzoid melanoma, no consensus has been reached (6,7). These new tools have provided further insight into these controversial lesions and can aid in their evaluation and further clinical approach.