[Nevus on nevus. Apropos of 7 case reports, 3 of them associated with other dysplasias, and 1 with an invasive malignant melanoma].

There is some doubt as to whether naevus pilus is identical with naevus-on-naevus or lentiginous naevus en mottes. The former could be classified together with Becker's naevus among the clinically progressive types of epidermal naevi, whereas the latter could be a truly melanocytic naevus of special expression which, for some authors, might become malignant. Seven cases of naevus-on-naevus with different sizes and locations are reported. In 3 cases the naevus was associated with other pathologies: pigmented sclerotic and kyphoscoliosis, verrucoid epidermal naevus, tuberous angioma and underlying muscular hypertrophy. In every case the diagnosis was confirmed by histological examination. An invasive malignant melanoma on superficial extensive melanoma coexisted with a retiform intradermal naevus pilosus. The hypothesis of complex neuro-ectodermic dysplasia and the histogenesis of malignant melanoma developed upon a naevus-on-naevus are discussed.