Proliferative Nodule With Unusual Features in a Giant Congenital Melanocytic Nevus

We describe a case of a newborn male with an erythematous friable nodule on a dorsolumbar giant congenital melanocytic nevus. Histopathology revealed a spindle cell neoplasm with a high mitotic index, negative for melanocytic markers, suggesting a mesenchymal tumor. However, genetic sequencing identified the NRAS Q16R mutation both in the nodule and underlying congenital nevus, leading to the diagnosis of a proliferative nodule composed of poorly differentiated melanocytes. Despite the limited use of molecular biology in the diagnosis of atypical proliferative nodules, it may be helpful in some challenging cases.