Cytoplasmic staining of erbB-2 but not mRNA correlates with differentiation in human thyroid neoplasia

Abstract

OBJECTIVE: Amplification and overexpression of the erbB-2 proto-oncogene in human carcinomas may have prognostic significance. Its role in thyroid carcinoma is controversial. We investigated human thyroid tumours for erbB-2 gene amplification, activating mutations in the transmembrane domain, quantitative mRNA expression and protein-expression. MATERIALS AND METHODS: DNA and mRNA were extracted from 47 morphologically characterized, frozen thyroid tumours including 10 nodular hyperplasias, 3 follicular carcinomas and 34 papillary carcinomas (4 with tall-cell features, 2 with insular and 2 with ariaplastic de-differentiation). DNA amplification was analysed by differential PCR. The transmembrane domain of erbB-2 was sequenced in all tumours for activating mutations in position 659. Levels of mRNA expression were determined by competitive mRNA RT-PCR. Immunohistochemistry (IHC) for erbB-2 protein expression in corresponding paraffin-embedded samples was evaluated. RESULTS: Our results showed no DNA amplification of erbB-2. Sequencing of the transmembrane domain of erbB-2 revealed no activating mutations. The level of mRNA expression was variable, 11 papillary carcinomas showing statistically significant elevated mRNA levels compared with corresponding normal thyroid tissue; however, this did not correlate with other indicators of poor prognosis. In contrast to elevated mRNA levels in tumours, the level of protein staining correlated with degree of differentiation, normal and hyperplastic tissue being strongly positive and poorly differentiated tumours negative. CONCLUSION: There are no mutations or amplifications of the erbB-2 gene in human thyroid tumours. Elevated erbB-2 mRNA expression in some thyroid tumours is not associated with clinical features of poor prognosis; however, the significance of the elevated mRNA levels is unclear, as it did not result in protein overexpression. Instead, cytoplasmic erbB2 protein detection by IHC correlates with differentiation of human thyroid tumours and may be a feature of good prognosis.