An atypical melanocytic lesion without genomic abnormalities shows locoregional metastasis.

A subset of difficult melanocytic lesions exists with histopathologic features that evade diagnostic consensus from even expert dermatopathologists. Comparative genomic hybridization (CGH) has emerged as a useful diagnostic tool to categorize these lesions, by identifying known chromosomal aberrations in malignant melanoma or the lack thereof in melanocytic nevi. However, determining a lesion's biological behavior primarily on CGH is limited by a relatively small series of corroborative cases without long term follow up. We present a case of a pigmented lesion on the right cheek of a 4 year old boy. The lesion had features of a deep penetrating nevus, but the presence of frequent mitoses, tumor infiltrating lymphocytes, and microscopic foci of tumor necrosis were concerning for an unusual melanoma. We termed this lesion a melanocytic tumor of uncertain potential (MELTUMP) for these reasons. High-resolution array-CGH performed elsewhere on the lesion demonstrated no melanoma-associated genomic abnormalities. A sentinel lymph node biopsy of this patient later revealed multiple small tumor deposits. Although the presence of nodal involvement in similar lesions often do not lead to progressive and fatal disease, this case illustrates that atypical melanocytic lesions with nodal involvement may not demonstrate genomic abnormalities by CGH, and that histopathologic assessment remains paramount in defining these difficult melanocytic lesions. Further comprehensive study of these lesions is needed.