Correlation of Immunohistochemistry and Fluorescence in Situ Hybridization for HER-2 Assessment in Breast Cancer Patients: Single Centre Experience

Abstract

Background: Accurate assessment of HER-2 is imperative in selecting patients for targeted therapy. Most commonly used test methods for HER-2 are immunohistochemistry (IHC) and fluorescence in situ hybridisation (FISH). We evaluated the concordance between FISH and IHC for HER-2 in breast cancer samples using Food and Drug Administration approved tests.

Material and methods: Archived paraffin tissue blocks from 73 breast cancer patients were used. HER-2 immunostaining was performed using Ventana anti-HER-2 monoclonal antibody. The FISH assay was performed using PathVysion™ HER-2 DNA Probe Kit.

Results: Of the 73 cases 68.5% were IHC 0/1+, 15.07% were IHC 2+ and 16.44% were IHC 3+. Successful hybridisation was achieved in 72 cases. HER-2 FISH amplification was determined in 16.67% cases. Ten IHC 3+ and two IHC 2+ cases were FISH positive. Two of the IHC 3+ cases were FISH negative. Concordance rate was 100%, 18.18% and 83.33% for IHC 0/1+, 2+ and 3+ group, respectively. Total concordance was 84.72%, kappa 0.598 (p < 0.0001). The sensitivity of IHC in detecting IHC 2+ and IHC 3+ cases was 16.7% and 83.3%, and the specificity was 85% and 96.67%, respectively.

Conclusion: The consistency between the methods was highest for IHC negative and lowest for IHC equivocal cases. The immunohistochemistry showed high sensitivity for IHC 2+/3+ cases and high specificity for IHC 3+ cases. Our results support the view that false-positive rather than false-negative IHC results are a problem with HER-2/IHC testing, and that IHC should be used as an initial screening test, but IHC 2+/ 3+ results should be confirmed by FISH.

Keywords: Breast cancer; Fluorescence in situ hybridisation; HER –2; Immunohistochemistry.

Figure 1

Distribution of HER-2 according to A, IHC (left) and B, FISH (right)

Figure 2

Typical examples of FISH-positive and FISH negative case. A, FISH amplified case, HER-2/Chr 17>2 (DAPI counterstain x 1000); B, FISH non amplified case, HER-2/Chr 17 < 2 (DAPI counterstain x 1000)

Figure 3

Discordance between IHC and FISH in two cases. Case 1: A, Invasive breast carcinoma (H&E x 200); B, HER-2/IHC 3+ (HER-2 x 200), C, FISH, HER-2/Chr 17 < 2, non amplified (DAPI counterstain x 1000). Case 2: D, Invasive breast carcinoma (H&E x 200); E, HER-2/IHC 3+ (HER-2 x 200); F, FISH, HER-2/Chr 17 < 2, non-amplified (DAPI counterstain x 1000)