Amplification of mutated NRAS leading to congenital melanoma in neurocutaneous melanocytosis.

The mechanisms behind malignant progression in patients with giant nevi are largely unknown. Here, we aim to describe novel genetic findings and explain possible mechanisms resulting in the most severe form of neurocutaneous melanocytosis. Detailed histological (biopsy and post-mortem) studies, tissue culture, and high-resolution cytogenetic analysis, including chromosome and array comparative genomic hybridization, Ion AmpliSeq Cancer Panel, and Sanger sequencing, were performed on tissues from a white male who succumbed at 17 months of age to congenital melanoma associated with a bathing-trunk nevus. We also used quantitative PCR to quantitatively assess the expression of NRAS among normal cells, including fibroblast and melanocytes, as well as melanoma cells from our patient. Full autopsy documented tumors in the brain, spinal cord, lung, liver, testis, bone marrow, and, retrospectively, in the placenta. Next-generation sequencing and chromosome microarray in our patient revealed novel findings, including duplication of a mutated NRAS gene, leading to an aggressive clinical course and disseminated disease. Quantitative PCR showed a five-fold increase in NRAS expression in the melanoma cell line when compared with normal melanocytes. Finally, three amino acid-changing germline variants were detected: homozygous TP53 p.P72R, heterozygous KIT p.M541L, and homozygous KDR (VEGFR2) p.Q472H. These genes are involved in malignancy and other potentially relevant pathways, such as mast cell and melanocytic signaling, as well as angiogenesis. These findings provide novel insights into the biology of congenital melanocytic proliferations, showing that amplification of mutated NRAS seems to represent a new genetic mechanism leading to melanoma in the context of neurocutaneous melanocytosis.