Monoplex LightCycler polymerase chain reaction quantitation of the HER2 gene for quality assurance of HER2/neu testing by immunohistochemistry and fluorescence in situ hybridization

Inconsistent Results With Different Secondary Reflex Assays for Resolving HER2 Status

OBJECTIVES

Guidelines suggest that secondary reflex testing may be useful for resolving HER2 status in breast cancers with equivocal results by both immunohistochemistry (IHC) and in situ hybridization (ISH). We compared two reflex ISH assays and a polymerase chain reaction (PCR) assay for this application.

METHODS

Twenty-nine breast cancers with equivocal IHC and ISH results were retested two ways: (1) ISH using differentially labeled probes targeting ERBB2 ( HER2 , 17q12) and either RAI1 (17p11.2) or ORC4 (2q22.3-2q23.1) in two separate assays and (2) real-time quantitative PCR amplification of ERBB2 and a control locus ( EIF5B , 2q11.2).

RESULTS

Results of the HER2 / RAI1 and HER2 / ORC4 ISH assays were concordant for 21 (72%) cases, and results of all three secondary reflex assays were concordant for only 18 (62%) cases. Result discrepancies between the two ISH readers were observed for cases close to the cutoff threshold.

CONCLUSIONS

Use of different control loci for ISH is associated with discordant results, and PCR is more likely to classify cases as nonamplified, possibly due to contamination with nontumor cells. While resolution of HER2 -equivocal results is desirable from a clinical perspective, different secondary reflex assays yield different results, and the correlation of these results with clinical outcomes is unknown.

Hybridization for human epidermal growth factor receptor 2 testing in gastric carcinoma: a comparison of fluorescence in-situ hybridization with a novel fully automated dual-colour silver in-situ hybridization method

Aims:

Amplification of the human epidermal growth factor receptor 2 (HER2) gene has been reported in gastric carcinoma (GC). Accordingly, trastuzumab plus chemotherapy has recently become the new standard treatment for HER2-positive advanced GCs. The aim was to compare the alleged gold standard for hybridization [fluorescence in-situ hybridization (FISH)] with a novel, fully automated brightfield dual-colour silver-enhanced in-situ hybridization (SISH) method.

Methods and results:

The studies series was comprised of 166 GC samples. Additionally, tumours with discordant results obtained by FISH and SISH were analysed by real-time quantitative polymerase chain reaction (PCR) with the LightMix kit HER-2/neu. Of the samples, 17.5% and 21% were amplified by FISH and SISH, respectively. Heterogeneity was identified in up to 52% of cases. In 96.4% of cases, FISH showed the same results as SISH. All six discordant cases were positive by SISH and negative by FISH. On review of the FISH slides, all contradictory cases were polysomic and were confirmed to be negative for amplification by real-time PCR. Interestingly, all ratios in this latter group were between 2.06 and 2.50, so setting the cut-off for amplification at ≥3 resulted in perfect concordance.

Conclusions:

Dual-colour SISH represents a novel method for the determination of HER2 status in GC.

Confirmation of a low HER2 positivity rate of breast carcinomas - limitations of immunohistochemistry and in situ hybridization

Background

Accurate assessment of the human epidermal growth factor receptor 2 (HER2) of invasive breast cancer is essential to treatment decisions since the advent of targeted therapy with the humanized monoclonal antibody trastuzumab and the dual tyrosine kinase inhibitor lapatinib. In the literature, the percentage of HER2-overexpressed/amplified breast carcinomas range from 3% to 30%. The routinely assigned low rate of 9% of HER2-overexpressed breast carcinomas alarmed one of our gynecologists who requested to confirm our HER2 test results.

Methods

A small study of 83 patients with breast carcinoma was designed to reexamine the routinely assessed HER2 status using immunohistochemistry and fluorescence in situ hybridization.

Results

The low rate of 9% of HER2-overexpressed/amplified breast tumors (DIN1C-3, invasive carcinoma) could be confirmed. However, FISH revealed two false positive cases and one false negative case. Moreover a case with an equivocal result in FISH was detected.

Conclusion

The HER2 positivity rate may be as low as 9%. The novel ASCO/CAP criteria for assessing immunohistochemical results in HER 2 testing reduce the false positive rate of HER2. First-line testing with immunohistochemistry may obscure false positive and false negative test results. In heterogeneous carcinomas even fluorescence in situ hybridization may not succeed in a correct evaluation of HER2.