Abstract

A 26-year-old female presented for evaluation of a large bump on her scalp that was present for two years. On physical examination, there was a 3 x 4 cm pedunculated tumor on the occipital scalp composed of blue-black and pink areas. An excisional biopsy demonstrated an atypical dermal proliferation of spindle cells arranged in fascicles and admixed with melanophages. There were several densely cellular, large nodules composed of spindle cells demonstrating cytologic atypia, mitotic activity, and areas of necrosis. The cellular proliferation demonstrated diffuse positivity for HMB45 and diffuse loss of p16. There was increased Ki-67/MART1 expression, areas of increased PRAME expression, and retained BAP1 expression. To better characterize the lesion, SNP chromosomal microarray analysis was performed on tissue microdissected from the atypical areas which demonstrated multiple abnormalities including a loss of chromosomes X and 1, a gain on 8q that included MYC, and a complex rearrangement on chromosome 10. The histological, immunophenotypical, and molecular findings supported a diagnosis of melanoma arising within an atypical cellular blue nevus. The patient underwent wide local excision with sentinel lymph node biopsy, which was negative for metastatic disease. Melanoma arising in blue nevi are uncommon tumors and distinction from an atypical cellular blue nevus on histopathology and immunohistochemistry alone can be challenging. In such cases, molecular diagnostic studies can be implemented to further characterize ambiguous lesions. Melanoma arising in cellular blue nevi more frequently demonstrates multiple chromosomal aberrations, which are also more likely to be complex, in comparison to atypical cellular blue nevi.