[Malignant transformation of a nevus of Ito: description of a rare case].

Dermal melanocytosis refers to congenital or acquired lesions characterized by the presence of dendritic cells derived from melanocytes that migrate from the neural crest to the epidermis. The nevus of Ito develops in the territory supplied by the acromioclavicular nerve. Malignant transformation in dermal melanocytosis is extremely rare, with only isolated case reports; only 2 cases of malignant transformation of a nevus of Ito have been reported. We report a very rare case that is the third to be described in the literature. The patient was a 24-year-old man who presented with a subcutaneous nodule that had developed in the anterolateral region of the thorax over the previous 8 months. The nodule was located beneath a faint blue-gray macule with poorly defined borders. Biopsy of the nodule revealed malignant melanoma; biopsies of the adjacent skin lesion showed a diffuse proliferation of scattered melanocytes in a collagen stroma in the reticular dermis. A diagnosis of malignant transformation of a nevus of Ito was made after other possibilities were ruled out.