Melanoma precursor lesions and borderline melanomas.

The histopathological interpretation of melanoma precursor and borderline lesions remains difficult. The natural history of naevi is reviewed and, in the light of this, current views on the histological sub-types of melanoma, precursor lesions and benign lesions which may mimic melanoma are presented. As the criteria for these lesions are now becoming defined they should be applicable by most histopathologists, even those who may see only occasional cases. Childhood and minimal deviation variants, however, are likely to remain problems even for the expert. Fortunately such lesions are uncommon.