Malignant melanoma on congenital naevus: a case of degeneration in a 6-month-old child with severe histological criteria.

Malignant melanoma in children is a rare and poorly understood pathology. We report a case of nodular melanoma that developed on congenital naevus in a 6-month-old infant. The histological results revealed a nodular melanoma on a congenital naevus measuring 6.625 mm in tumour thickness according to Breslow. The infant was treated by broad resection without adjuvant treatment. Follow up is 43 months without metastasis. Malignant melanoma is a rare pathology: 1-4% of all melanomas occur before the age of 20 and 0.3-0.4% of those are before puberty. The risk of degeneration of a congenital naevus into a melanoma is approximately 0.7%. Surgical exeresis must be broad. Up to now, no complementary treatment has proven to be effective. Pre-operative examination for sentinel lymph nodes by lymphography can be of interest although such an examination is difficult in children. The prognosis would appear to be similar to that of malignant melanoma in adults with a high mortality. This is therefore an argument in favour of early treatment and prolonged follow up of children with malignant melanoma.