PTGS2 and melanoma: Moreover, as shown by immunohistochemistry, COX-2 expression in primary melanomas is restricted to melanoma cells and significant correlation between immunohistochemical staining, tumor thickness and disease-specific survival has been reported [24], suggesting that COX-2 is a prognostic marker and a potential therapeutic target, although its role in the complex pathogenic process of bone metastasis is unclear [3].