Background: Women with HER2-overexpressing breast cancer have an unfavorable prognosis. Trastuzumab improves survival when combined with chemotherapy in the first-line treatment of patients with HER2-overexpressing metastatic breast cancer and decreases the rate of disease relapse by 52% and the rate of death by 33% in women with HER2-overexpressing early-stage breast cancer. HER2 testing can be performed using immunohistochemistry (IHC) or fluorescence in situ hybridization (FISH) and can be performed at local pathology laboratories or at central/reference laboratories. Because of the significant benefit seen with trastuzumab, it is critical to accurately identify women most likely to benefit. The method and the location of HER2 testing contribute to the accuracy of test results.
Patients and methods: HER-First, a prospective, community-based, phase IV study of first-line trastuzumab/taxane therapy, enrolled patients with HER2-overexpressing metastatic breast cancer. Retesting of all tumor specimens by HER2 IHC and FISH at a high-volume, experienced laboratory was required.
Results: Concordance between local and central laboratory HER2 IHC testing was highest for local IHC 3+ samples (n = 377; 77%) and lowest for IHC 2+ samples (n = 184; 26%). Thirty-three percent of samples testing IHC 2+ at a local laboratory tested FISH-positive at the central laboratory. Concordance between HER2 IHC and FISH results was higher when both tests were performed at the central laboratory.
Conclusion: Accurate HER2 test results are critical to identify patients who are appropriate candidates for trastuzumab, a therapy with significant clinical benefits in HER2-overexpressing breast cancer. These data show that HER2 testing is most accurate when performed at a high-volume reference laboratory.