Molecular and immunohistochemical analysis of ERBB2 expression in correlation with proliferation rate in synovial sarcoma.

The aim of the study was to determine whether or not the tyrosine kinase receptor ERBB2 is overexpressed in synovial sarcomas (SSs). We also focused on the cell cycle-related nuclear protein-Ki-67. Thirty-two samples were available for immunohistochemistry and only 1 case revealed a weak diffuse membrane ERBB-2 staining. The remaining cases showed either no staining (20 cases) or weak focal membrane staining (9 cases). In our 3 highly overexpressed ERBB2 mRNA samples, fluorescence in situ hybridization showed no amplification of the ERBB2 gene. ERBB2 mRNA expression was present in all samples of SSs at a comparable level to that in breast carcinoma control group, with a 2+ or 3+ immunopositivity. The high level of ERBB2 mRNA expression correlated with a high level of Ki-67 mRNA. The level of Ki-67 mRNA correlated with Ki-67 protein expression. The study shows that ERBB2 mRNA expression is very strong in SSs, but the membrane ERBB-2 protein expression is practically absent.