The HercepTest and routine C-erbB2 immunohistochemistry in breast cancer: any difference?

The proto-oncogene c-erbB2, located on chromosome 17q21, encodes a 185-kD transmembrane glycoprotein. It is known to be overexpressed, amplified, or both in 20% to 30% of breast cancers. C-erbB2 belongs to the human epidermal growth factor receptor (tyrosine kinase receptor) family that plays an important role in cell cycle regulation and differentiation. Although there are various methods to assess c-erbB2 status in breast cancer, protein overexpression determined by immunohistochemistry and gene amplification using fluorescence in situ hybridisation are most commonly utilised. This study compares the results of the DAKO HercepTest with the immunohistochemical assay (A0485, DAKO), which is routinely used in our pathology laboratory.

Paraffin-embedded breast cancer tissues from 41 patients operated in a tertiary hospital during the year 2000 were subjected to immunohistochemistry by the above methods. C-erbB2 positivity was defined by cytoplasmic membrane staining of 2+ or 3+ intensity.

Overexpression of c-erbB2 protein was present in 36.6% and 41.5% of cases when detected by HercepTest and the DAKO A0485 antibody, respectively. There was almost perfect agreement between both methods (k = 0.898) when positive versus negative results were considered, and moderate agreement in terms of individual staining intensities (k = 0.554).

Routine immunohistochemistry using the DAKO A0485 antibody is a reliable, cost-effective alternative to the HercepTest in determining prognosis and suitability of patients for Herceptin therapy.