The intermediate filament peripherin is expressed in cutaneous melanocytic lesions.

Peripherin is an intermediate filament involved in growth and development of the peripheral nervous system and is localized to neurons, some other cells derived from neural tube and neural crest, and some neuroendocrine cells (e.g. beta cells of islets of Langerhans). Peripherin also has been demonstrated in neuroblastomas and cutaneous neuroendocrine (Merkel cell) carcinomas. The expression of peripherin by other cells derived from the neural crest is unknown. We evaluated by immunohistochemistry 74 cutaneous melanocytic lesions including primary invasive malignant melanoma (IMM), melanoma in situ (MIS), atypical nevus (nevus with architectural disorder and cytologic atypia of melanocytes) (AN), spindle and epithelioid cell nevus (Spitz nevus) (SN), blue nevus (BN), and common intradermal benign melanocytic nevus (BMN) for expression of peripherin. Peripherin was detected in a cytoplasmic distribution within tumor cells in 14/14 IMM and 8/10 MIS. For IMM, peripherin localized to both the intraepidermal and invasive dermal components. Peripherin was detected in 10/10 AN and 9/9 SN, being localized to the intraepidermal component and, focally, to the superficial dermal component of the lesions. The dendritic nevus cells in 15/15 BN also expressed peripherin. For most of the BMN, expression of peripherin was absent or limited to rare, scattered cells in the superficial portion of the lesions. Melanocytes in adjacent normal skin were not labeled in any of the lesions studied. These results indicate that expression of peripherin is common in both benign and malignant melanocytic lesions, but not in normal resting adult melanocytes. Among benign lesions, expression of peripherin in the dermal component is rare except in the dendritic cells of BN. These findings provide evidence that the expression of peripherin, a marker of neuronal differentiation, is maintained by IMM, MIS, and BN, but is lost in the normal maturational sequence of the dermal component of other melanocytic lesions.