Malignant blue nevus. Report of four new cases and review of the literature.

Malignant blue nevus is a rare melanotic tumor of the skin arising from a pre-existing blue nevus. To date only few cases have been reported. The diagnosis of malignant blue nevus is frequently difficult. Generally accepted criteria do exist, but their application may be controversial. The present paper reports four new cases of malignant blue nevus with follow-up of 3-5 years. Our present data, along with those of the literature, suggest that malignant blue nevus may be more aggressive than generally thought.