Multiple agminate Spitz naevi: review of the literature and report of a case with distinctive immunohistological features.

We describe a 13-year-old girl with multiple pigmented nodules and plaques arranged in a cluster in the right lumbar region, which had developed since infancy. Eleven of 15 lesions which were examined histologically were found to be Spitz naevi. The remaining four lesions were compound naevocellular naevi, and two of them showed focal dysplasia. Eight Spitz naevi were investigated immunohistologically with monoclonal antibodies against HLA-antigens and malignancy-associated melanocytic antigens which are rarely present in common naevi. Naevus cells in all lesions expressed HLA-ABC antigens, but lacked HLA-DR antigens in seven of the eight lesions. All naevi were positive for 'constitutive' (KG-6-56) and 'early' (K-1-2) markers of naevomelanocytic cells. In five of the eight Spitz naevi, at least one of the three malignancy-associated melanocytic antigens PAL-M1, A-1-43 and A-10-33 was found. The expression of malignancy-associated antigens in multiple agminate Spitz naevi is at variance with their benign clinical course.