Evaluation of the United States Food and Drug Administration-approved scoring and test system of HER-2 protein expression in breast cancer.

PURPOSE: The purpose of this study was to investigate the prognostic significance of assessment of human epidermal growth factor receptor (HER)-2 oncogene protein overexpression of breast cancer tissue by the United States Food and Drug Administration (FDA)-approved HercepTest and grading system (negative, 0 or 1+; weakly positive, 2+; strongly positive, 3+). Furthermore, results of the HercepTest were correlated with immunohistochemical results obtained using different antibodies and protocols and with HER-2 oncogene gene amplification assessed by fluorescence in situ hybridization (FISH). EXPERIMENTAL
DESIGN: HER-2 status in 303 patients with lymph node-positive breast cancer was investigated by using a rabbit polyclonal antibody (DAKO) by conventional immunohistochemistry and by applying the HercepTest. Furthermore, the monoclonal antibody CB-11 was used in conventional immunohistochemistry and with the NexES automatic stainer, which is also under consideration for FDA approval for determination of eligibility for Herceptin therapy. Results were compared with FISH analysis performed in all 2+ and 3+ specimens (103 cases) and 104 HER-2-negative specimens.
RESULTS: 3+ positive carcinomas were found in 8.9-15.7% of specimens. FISH revealed that almost exclusively 3+ positive cases were amplified, with the HercepTest and the NexES automatic stainer giving the best results. In univariate analysis, staining with the HercepTest revealed a significantly worse prognosis in 3+ cases. Also, 3+ cases were significantly associated with lower estrogen receptor levels and histological grade III tumors.
CONCLUSIONS: This study shows that the results of the FDA-approved HER-2 grading and test system correlated strongly with findings in FISH. Furthermore, HercepTest proved to be of prognostic relevance. Strict adherence to the given protocols is critical.