HER2 testing by local, central, and reference laboratories in the NCCTG N9831 Intergroup Adjuvant Trial

567 Background: N9831 is evaluating trastuzumab as adjuvant therapy for patients with HER2 positive resected breast cancer. Accurate determination of HER2 status is essential to select patients most likely to benefit from therapy. An earlier report from this study found poor concordance between HER2 findings of local laboratories and central laboratory (JNCI 94:855,2002). Eligibility criteria were modified in early 2002 to require central review for HER2 status. This report provides data of HER2 testing concordance following this modification. Methods: Eligible women were allowed entry to N9831 based on the local laboratory determination that the tumor was strongly HER2+ by immunohistochemistry (IHC) or HER2 gene amplification by fluorescence in situ hybridization (FISH). Local laboratory testing was confirmed by central testing (Mayo Clinic) using IHC (Dako Herceptest™) and FISH (Vysis PathVysion™). Cases where central testing results were not 3+ by IHC and not amplified by FISH (HER2:CEP17 ratio <2) were sent to another reference laboratory (LabCorp) for testing. Results: 967cases were reviewed by the central laboratory. Local testing methods included IHC (49% HercepTest™ and 26% non-HercepTest™) and FISH (25%). There were 827 (85.5%) patient samples found to be either 3+ or FISH+ by central testing. Concordance between central and local testing when the same method was used was 79% for HercepTest™, 69% for non-HercepTest™, and 85% for FISH. Of the 140 discordant cases, 130 were re-tested at LabCorp and 10 cases (7.7%) were discordant, i.e., found to be 3+ or FISH+. The agreement between central review and LabCorp was 97% (126/130) for IHC (0,1+ or 2+) and 95.2% (119/125) for FISH (not amplified). Conclusions: There was a high level of discordance between local and central laboratories for both IHC and FISH. When a reference laboratory tested the discordant cases, there was high degree of agreement in both the IHC and FISH findings. These data show that HER2 testing by experienced laboratories improves patient selection for trastuzumab therapy. Supported by the Breast Cancer Research Foundation, Genentech, National Cancer Institute (CA25224). Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Eli Lilly; Merck; Pfizer; Vysis, Inc.; Wyeth Merck Aventis; Pfizer; Sanofi Genentech