Accuracy of the determination of S100 protein expression in malignant melanoma using a polyclonal antibody directed against S100 and monoclonal antibodies specific for S100 alpha and beta

Abstract

S100 proteins are present in a variety of tissues and perform regulatory functions in numerous metabolic processes. They have an important role in many human cancers, including malignant melanoma. Both polyclonal and monoclonal antibodies have been used to investigate S100 expression in melanoma tissue sections. This study aimed to determine the accuracy and sensitivity of these two types of antibodies in detecting S100 proteins in paraffin processed tissue cases of malignant melanoma. The study compared routinely used rabbit polyclonal anti-S100 antibody raised against both anti-S100A and B isoforms (Dako, Glostrup, Denmark), as per studies by Timar, and compared and contrasted findings with mouse monoclonal anti-S100A and anti-S100B antibodies (Santa Cruz Biotechnology, Inc., Santa Cruz, CA, USA). The study involved the assessment of formalin-fixed paraffin-embedded tissue blocks from 56 cases of malignant melanoma, consisting of 23 superficial spreading, nine nodular, eight lentigo maligna, five acral lentigenous forms, five metastatic melanomas (two sentinel lymph node positive cases and three cases of nodal involvement from cases of elective nodal groin dissections), and six cases of desmoplastic malignant melanoma (DMM). The slides were stained by immunohistochemical methods on an automated platform (BenchMark XT; Roche, USA) and employing the iView detection system. All slides were examined by routine light microscopy by two independent assessors. The best results for both intensity of staining and percentage of positive tumor cells were achieved with polyclonal anti-S100 antibody and monoclonal anti-S100B antibody. Anti-S100A antibody yielded weaker staining intensity (with mean intensity of 1·8, compared to 2·8 for both anti-S100B antibody and polyclonal anti-S100 antibody), and a lower percentage of positive melanoma cells (an average of 74% for anti-S100A, compared to 95% for both anti-S100B antibody and polyclonal anti-S100 antibody). This result was statistically significant (P<0·01). Staining in cases of DMM gave the same results (P<0·01). The conclusion from this study is that polyclonal anti-S100 antibody and monoclonal anti-S100B antibody are more suitable than monoclonal anti-S100A antibody for diagnostic investigations of malignant melanoma, irrespective of the histological type of melanoma.