Non-melanocytic lesions mimicking melanocytic lesions.

Distinction between benign and malignant melanocytic lesions commonly represents a big challenge for the pathologist. Equally difficult is separating tumours with melanocytic lineage from those displaying other lines of differentiation. This is because benign and malignant melanocytic lesions are able to display a wide range of histological appearances that frequently closely mimic reactive and neoplastic lesions (benign and malignant). This applies to processes with almost any line of differentiation. Difficulties in differential diagnosis are mainly found in melanocytic lesions restricted to the dermis or those in which the junctional component is minimal. Although purely junctional melanocytic lesions less commonly pose a problem in differential diagnosis, they may be very problematic, especially in small biopsies. Immunohistochemistry is usually a very important aid in the differential diagnosis of mimics of melanocytic lesions but pitfalls often occur. This is particularly true when small samples are analysed and when close clinicopathological correlation is lacking. This review discusses the histological differential diagnosis of mimics of melanocytic lesions. These mimics are separated into those primarily presenting in the epidermis and those presenting in the dermis.