Schuler A, Smith M, Zahn J, et al. - Researchers reported the case of a 52-year-old female with an Atypical Spitz tumor (AST) in which array-based comparative genomic hybridization (aCGH) was critical in guiding exact diagnosis and management. The first presenting complaint was a flesh-colored papule on her arm that was changing color. Biopsy showed a dermal nevoid melanocytic tumor of indeterminate histopathology, favored to be a harshly atypical nevus. The excision of the tumor was performed. One year later, they performed a biopsy on another flesh-colored papule proximal to the excision site of the first tumor. The finding revealed a mainly dermal atypical spitzoid melanocytic proliferation with a differential diagnosis of AST vs spitzoid melanoma. Molecular analysis of both lesions by aCGH exhibited different molecular signatures, supporting the 2 tumors to be clonally not related. Moreover, the new tumor revealed limited proof of genomic instability, supporting classification as an AST with prognosticated indolent behavior. Therefore, this case highlights the advantage of aCGH in assessing borderline melanocytic lesions, involving assessment of malignant potential in ASTs, and clonality examination to assist in the exclusion of metastatic disease.