MSG-1 expression in benign and malignant melanocytic lesions of cutaneous and mucosal epithelium

A more recently characterized melanocyte-specific gene, MSG-1, has been suggested as having a role in embryogenesis, melanogenesis and melanoma progression. Studies involving MSG-1 have involved cutaneous melanocytic lesions, which are different than non-cutaneous melanocytic lesions in certain pathogenetic aspects. The purpose of this study was to evaluate MSG-1 protein expression in cutaneous and mucosal melanocytic lesions, with the aim to explore its association with pigment production, malignant potential and UV light exposure.

Benign and malignant melanocytic lesions of cutaneous and mucosal epithelium were selected from our pathology registry (n=48). Immunohistochemistry was performed using polyclonal anti-MSG-1 antibody and standard streptavidin-biotin immunoperoxidase techniques. The staining pattern of MSG-1 was evaluated by three pathologists independently.

MSG-1 protein demonstrated immunoreactivity in only one mucosal melanoma (1/20, 5%), arising in the lower lip, and showing histopathologic evidence of sun-induced tissue damage. MSG-1 also showed positivity in five cutaneous melanomas (5/14, 36%), one of which was a metastatic lesion. All mucosal and cutaneous nevi failed to express MSG-1. Melanin pigmentation, seen in 18/34 melanoma and 13/14 nevi, did not correlate with MSG-1 expression. All cases but one showing MSG-1 immunoreactivity were located in sun-exposed sites.

The finding of MSG-1 expression in some cases of malignant melanoma, and its absence in all benign nevi, may indicate an association with melanoma progression, particularly UV-induced lesions. Its infrequent expression in melanocytic lesions limits its diagnostic value as an immunohistochemical marker in routine pathology practice.