Chen, B.

e11527 Background: 118 Her2 positive invasive carcinomas were retested centrally at the Mayo Clinic for Her2 status confirmation prior to inclusion in Mayo Clinic Cancer Research Consortium study RC0639 phase II study of cardiac safety and tolerability of adjuvant chemotherapy plus trastuzumab with lapatinib for resected Her2+ breast cancer (MCCRC RC0639). Methods: Central confirmatory methods were immunohistochemical (IHC) Dako HercepTest on a Dako Autostainer using the manufacturer's recommendations and HercepTest kit epitrope retrieval kit and fluorescent in situ hybridization (FISH) using Vysis PathVysion probe kit. Test results are interpreted using ASCO/CAP guidelines (IHC >30%, Her2:CEP 17 ratio >2.2). Results: There is local and central test 3+ IHC concordance in 48 of 53 tumors (agreement 90.6%) and FISH amplification in 29 of 33 tumors (agreement 87.9%), improved or similar results using identical methods to results in NCCTG N9831 adjuvant trial (n=1063, 81.6% IHC; n=813, 88.1% FISH). Of 92 centrally tested 3+ IHC positive tumors, 88 (95.7%) were FISH amplified. 5 centrally tested patients interpreted as Her2 positive by pre-ASCO/CAP guidelines (IHC >10%; HER2:CEP17 ratio >2) are Her2 ineligible using ASCO/CAP guidelines. IHC not confirmed centrally was reviewed by a second pathologist in 16 of 118 specimens. IHC concordance between two central pathologists was 10/16 (62.5%) in negative or equivocal (≤30% IHC staining) specimens; 7/10 (70%) with two reader agreement were FISH amplified and 4/6 (66%) with disagreement were FISH amplified. Conclusions: Concordance in IHC and FISH results between local and central labs is similar or improved since N9831. New ASCO/CAP Her2 testing guidelines change eligibility based on Her2 status in 4.2 % of patients. Equivocal IHC results falling between pre- and post- ASCO/CAP IHC positive thresholds (>10% and <30% IHC strong staining) are only partially resolved by repeat IHC review and/or FISH testing. No significant financial relationships to disclose.

Abstract Background: In 2007, the American Society of Clinical Oncology and College of American Pathologists (ASCO/CAP) recommended new guidelines to define HER2 positivity by immunohistochemistry (3+ IHC: uniform intense membrane staining of &gt;30% of invasive tumor cells) or fluorescent in situ hybridization (FISH+: HER2/CEP17 ratio &gt;2.2). The original criteria used for enrollment in the pivotal N9831 trial conducted from 2000-2005 were IHC&gt;10% (3+) or FISH ≥2.0.Purpose: To investigate the impact of the ASCO/CAP guidelines on patient (pt) eligibility and disease free survival (DFS) compared to the originally used FDA-approved definitions.Patients/Methods: This analysis included 2268 patients from the HER2+ N9831 adjuvant trastuzumab phase III trial. IHC was centrally performed at the Mayo Clinic using the DAKO HercepTest™ and was re-analyzed to determine the percent of tumor cells with 0, 1+, 2+, and 3+ staining intensities. DFS was compared between pts randomized to standard chemotherapy +/- concurrent trastuzumab (Arms A and C of the trial) within IHC/FISH subgroups using Cox proportional hazards regression stratified by hormone receptor and nodal status.Results: Based on 2268 pts, 83 pts (3.7%) were 3+ by FDA-approved guidelines but not 3+ by the ASCO/CAP guidelines. Among these pts, 77% (64/83) were FISH amplified centrally by ASCO/CAP guidelines. Only 1.5% (34/2268) of pts eligible under FDA-approved definitions from N9831 in this sample set would not meet the ASCO/CAP guidelines. In 1441 patients randomized to standard chemotherapy +/- concurrent trastuzumab, the exploratory DFS hazard ratio (HR) associated with trastuzumab in IHC/FISH subgroups were as follows: ASCO/CAP HER2+ HR=0.59 (95% CI: 0.47-0.75; p&lt;0.001); FDA-approved HER2+ HR=0.60 (95% CI: 0.47-0.75; p&lt;0.001); ASCO/CAP HER2 normal(not positive) HR=0.74 (95% CI: 0.35-1.57; p=0.43); and FDA-approved HER2 normal HR=0.53 (95% CI: 0.22-1.26; p=0.15).Conclusions: A small percentage (1.5%) of N9831 patients did not meet ASCO/CAP 2007 guidelines when applied retrospectively. Trastuzumab effect appeared similar for HER2+ patients regardless of ASCO/CAP or FDA-approved guidelines. Additional DFS analyses by IHC/FISH subgroups will be presented. We gratefully acknowledge support from the Breast Cancer Research Foundation, Genentech, and NIH CA25224 for this study. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 701.