Automated Silver-enhanced In Situ Hybridization for Evaluation of HER2 Gene Status in Breast Carcinoma: Comparison with Fluorescence In Situ Hybridization and Immunohistochemistry

ABSTRACT

BACKGROUND: The human epidermal growth factor receptor 2 (HER2) is amplified in 20-25% of breast cancers. HER2 overexpression or amplification is associated with a worse clinical outcome and it can predict the benefit from anthracycline and anti-HER2 therapies. The HER2 status has usually been assessed by immunohistochemistry (IHC) or fluorescence in situ hybridization (FISH) in clinical samples. A new silver-enhanced in situ hybridization (SISH) technique was recently introduced. Therefore we evaluated the usefulness of SISH for detecting HER2 amplification. METHODS: Tissue microarrays (TMAs) were constructed with 144 invasive breast cancer tissue samples. We performed IHC, FISH and SISH for HER2 on the tissue sections from the TMAs and we interpreted the results according to the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) guidelines. The concordant rates between the two different tests were calculated. RESULTS: HER2 was overexpressed and amplified in 16.9%, 16.9%, and 18% of the cases by IHC, FISH and SISH, respectively. The concordant rates between IHC and FISH, IHC and SISH, and FISH and SISH were 95.1%, 95.7%, and 97.8%, respectively. CONCLUSIONS: SISH can be an alternative test for evaluating HER2 amplification because the 97.8% concordance with FISH satisfies the ASCO/CAP requirement of > 95% concordance with an alternative validated method.