[The role of new molecular tests in the diagnosis of melanoma in a setting of congenital nævus in an infant].

Congenital and infantile melanomas are extremely rare. We report a case of a child presenting at birth with a giant congenital nevus complicated by melanoma and on long-term follow-up with exploration using new immunohistochemistry and molecular biology tools. A new-born girl presented at birth with a large congenital cervico-mandibular tumour with para-pharyngeal extension and underlying osteolysis. At 7 months, histology and immunohistochemistry of the operative specimen revealed nodules with atypical features (mitotic figures, necrosis and positive expression of KI67 and P53 in approximatively 50 % of the melanocytic nuclei). A diagnosis was made of infantile melanoma associated with congenital nevi. Repeated surgery and monitoring (clinical and imaging) were performed. At the age of 7 years, as there was no evidence of metastatic lesions, further analyses were performed on the initial operative specimen. Investigation of transcription factor expression using immunohistochemistry, comparative genomic hybridization and histology-guided mass spectrometry, although suspect, did not in itself support a diagnosis of melanoma. Finally, at the age of 7 years, hepatic and pulmonary metastases were reported. Despite combined immunotherapy with ipilimumab and nivolumab, the child died 5 months later. This case illustrates the complexity of diagnosis of infantile melanoma and the risk of metastatic involvement long after the initial diagnosis. Diagnosis may be difficult and necessitates expert advice and the application of several recent methods to reach a conclusion and initiate appropriate treatment.

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