Accuracy of the determination of S100B protein expression in malignant melanoma using polyclonal or monoclonal antibodies

Aims: To compare the routinely used polyclonal anti-S100 and a mouse monoclonal anti-S100B antibody for their accuracy in the detection of the S100B expression profile (pattern and intensity) in a series of 67 primary (n = 37) and lymph node metastatic (n = 30) melanoma tissues. S100B is the lineage marker of malignant melanoma. Antibodies routinely used for melanoma diagnosis are not necessarily specific for this protein. Furthermore, clinical monitoring of melanoma progression is mostly based on the determination of serum S100B protein levels without knowing the actual expression level in the primary and/or metastatic tissue. Methods and results: The profile of expression patterns (focal, heterogenous and diffuse) as well as intensity ranges (+, ++ and +++) were similar for the two antibodies in melanoma tissues. However, comparison of the patterns and intensities on the basis of individual cases revealed a high frequency of discrepancies (50.7 and 58.2%, respectively). Severe discrepancy between the two antibodies in the determination of the S100B protein expression pattern (focal versus diffuse or focal versus heterogeneous) was relatively frequent; 13.4 and 11.9%, respectively. Furthermore, a similar rate of severe discrepancy was observed between the two antibodies in the determination of the intensity of S100B expression levels (+ versus +++ or + versus ++); 19.4 and 8.9%, respectively. Separate analysis of the primary tumours and metastases gave similar results. Conclusion: For the accurate determination of S100B protein expression in malignant melanoma it is highly recommended that a monospecific antibody is used.