[307] Negative HER-2 by Immunohistochemistry Correlates Strongly with Negative HER-2 Amplification by Fluorescence In Situ Hybridization in Triple Negative Breast Cancers

Rena Xian, Puthiyaveettil Raghunath, Zhang Paul. Hospital of the University of Pennsylvania, Philadelphia, PA

Background: Immunohistochemistry (IHC) and fluorescence in-situ hybridization (FISH) are the two most commonly applied techniques for determining HER-2 status on routine breast cancer (BRCA) specimens. Due to its cost and technical complexity, many laboratories reserve FISH as a confirmatory test for equivocal IHC results. Although, in general IHC and FISH have been shown to have excellent concordance in determining HER2 status by some investigators, others still contend that FISH should be performed in all BRCA regardless of IHC results, as occasional IHC-/FISH+ cases have been found. However, it is unclear if these cases are luminal A type BRCA or triple negative breast carcinomas (TNBC). Our institution performs FISH routinely on all cases of TNBC. This allowed us to evaluate a large number of TNBC cases for the probability of HER-2 amplification by FISH when IHC staining is negative.
Design: Predictive markers were tested by Dako HercepTestTM and Dako ER/PR pharmDXTM on all primary invasive breast carcinomas on the Dako autostainer. FISH was performed by standard techniques using the Vysis Her-2 DNA probe kitTM. HER-2 is considered amplified when the HER-2/CEP17 ratio is >2.2 or HER-2/cell is >6. HER-2/CEP17 ratios between 1.8-2.2, and HER-2 copies/cell of 4-6, are considered equivocal. TNBC were identified from our laboratory database, and the corresponding IHC and FISH results were tabulated. As controls, we also performed the same analysis on all equivocal HER-2 cases by IHC from the same time period.
Results: From 2009-2011, a total 112 TNBC were identified, which had follow-up HER2 FISH analysis. FISH was also performed on 72 IHC equivocal cases from the same period. See Table 1 for IHC and FISH correlation.

Table 1. HER-2 status by IHC correlates with FISH results, with a p-value of <0.0001 (n=206).
 FISH NEG (%)FISH Equivocal (%)FISH POS (%)
IHC NEG109 (97.3%)2 (1.8%)1 (0.9%)
IHC Equivocal61 (84.7%)4 (5.6%)7 (9.7%)
The HercepTest was repeated on IHC-/FISH+ cases and remained negative by IHC.


Conclusions: Our results indicate a strong correlation between IHC and FISH analysis of HER-2 expression in TNBC. HER2 gene amplifications by FISH is very rare in TNBC (<1%). In addition to possible technical failure in IHC (true false IHC results), this discrepancy could also be explained by various translational events. Our data suggests that HER2 amplification is very uncommon in TNBC.
Category: Breast

Tuesday, March 5, 2013 1:00 PM

Poster Session IV # 46, Tuesday Afternoon

 

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