High Concordance between HercepTest IHC and HER2 FISH: An Analysis of Two Companion Diagnostic Tests before and after Implementation of ASCO/CAP 2007 Guidelines
Maria E Vergara-Lluri, Neda A Moatamed, Sophia K Apple. David Geffen UCLA Medical Center, Los Angeles, CA
Background: Human epidermal growth factor receptor 2 (HER2) is a critical predictive marker in patients with invasive breast cancer who can benefit from treatment with trastuzumab. It is thus imperative to ensure accuracy and precision in HER2 testing. In 2007, The American Society of Clinical Oncology/College of American Pathologists ASCO/CAP guidelines proposed new recommendations for HER2 testing for IHC and FISH scoring in an effort to improve accuracy and utility of these companion diagnostic tests as a predictive marker for patients with invasive breast cancer. The goal of the new guidelines was to improve the concordance rate between the diagnostic tests for HER2 and decrease the number of inconclusive cases.
Design: Both IHC and HER2 FISH were performed on all specimens from our facility from years 2003 through 2011 (n=1447). Cases from 2003 to 2007 (n=958) were scored by FDA guidelines prior to publication of ASCO/CAP guidelines, with IHC 3+ cases staining >10% of tumor cells and FISH amplification cutoff value of 2.0. The new ASCO/CAP guidelines were implemented and scored accordingly for cases from 2008 to 2011 (n=489), with IHC 3+ cases staining >30% of tumor cells and FISH amplification cutoff value of 2.2. We compared the concordance rates before and after ASCO/CAP guidelines to see if ASCO/CAP guidelines yielded improvement in concordance rate between IHC and FISH.
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