Background: A more recently characterized melanocyte-specific gene, MSG-1,has been suggested as having a role in embryogenesis, melanogenesis and melanoma progression. Studiesinvolving MSG-1 have involved cutaneous melanocytic lesions, which are different than non-cutaneous melanocyticlesions in certain pathogenetic aspects. The purpose of this study was to evaluate MSG-1 protein expressionin cutaneous and mucosal melanocytic lesions, with the aim to explore its association with pigment production,malignant potential and UV light exposure. Material/Methods: Benign and malignant melanocytic lesionsof cutaneous and mucosal epithelium were selected from our pathology registry (n=48). Immunohistochemistrywas performed using polyclonal anti-MSG-1 antibody and standard streptavidin-biotin immunoperoxidasetechniques. The staining pattern of MSG-1 was evaluated by three pathologists independently. Results:MSG-1 protein demonstrated immunoreactivity in only one mucosal melanoma (1/20, 5%), arising in the lowerlip, and showing histopathologic evidence of sun-induced tissue damage. MSG-1 also showed positivityin five cutaneous melanomas (5/14, 36%), one of which was a metastatic lesion. All mucosal and cutaneousnevi failed to express MSG-1. Melanin pigmentation, seen in 18/34 melanoma and 13/14 nevi, did not correlatewith MSG-1 expression. All cases but one showing MSG-1 immunoreactivity were located in sun-exposed sites.Conclusions: The finding of MSG-1 expression in some cases of malignant melanoma, and its absence inall 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 immunohistochemicalmarker in routine pathology practice.

Keywords: Melanocytes - metabolism, Melanoma - metabolism, Melanoma - pathology, Mouth Neoplasms - metabolism, Mouth Neoplasms - pathology, Mucous Membrane - metabolism, Mucous Membrane - pathology, Nuclear Proteins - biosynthesis, Skin - metabolism, Skin - pathology, Skin Neoplasms - metabolism, Skin Neoplasms - pathology, Trans-Activators - biosynthesis, Transcription Factors, Melanocytes - metabolism, Melanoma - pathology, Mouth Neoplasms - pathology, Mucous Membrane - pathology, Nuclear Proteins - biosynthesis, Skin - pathology, Skin Neoplasms - pathology, Trans-Activators - biosynthesis, Transcription Factors