Ca(2+)-binding proteins S100A6 and S100B in primary cutaneous melanoma

Commercially available polyclonal antibodies against a mixture of bovine brain S100 proteins have become an established marker for immunohistochemical characterization of malignant melanoma. However, the commercially available antibodies used are undefined and to date, 13 different human S100 proteins are known. The purpose of this study was to examine the expression of 4 newly available polyclonal antibodies against the human recombinant Ca(2+)-binding S100 proteins, S100A1, S100A2, S100A4 and S100A6, in cutaneous melanoma and to correlate these findings with the standard S100 staining as well as with the metastatic potential of the primary.

39 formalin-fixed paraffin-embedded primary cutaneous melanomas were incubated with polyclonal antibodies against recombinant human S100 proteins using the APAAP method. The extent of staining was qualitatively assessed and a staining index was calculated. Findings were correlated to the metastatic potential and the overall survival in all patients.

Staining with antibodies against human S100A6 as well as with antibodies against conventional bovine S100 proteins was positive in all specimens. No correlation was found between the extent of protein expression and patients' outcome for standard S100 staining as well as for S100A6. S100A1, S100A2 and S100A4 staining could not be used for statistical analysis due to their low expression in melanoma.

Staining was positive using S100A6 antibodies in all specimens, the quality being inferior to the commercially available S100 antibody. Highly specific and well characterized antibodies against the individual S100 proteins are now available for future immunohistochemical characterization studies in melanomas.