50P Silver-Enhanced in Situ Hybridization as an Alternative to Fluorescence in Situ Hybridization for Assaying Her2 Amplification in Clinical Breast Cancer

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ABSTRACT Purpose Valid determination of HER2 status is a prerequisite to establish adequate treatment strategy for breast cancer patient regardless of the disease stage. The goal of this study was to examine the feasibility of the newly developed silver-enhanced in situ hybridization technique as an alternative to fluorescence in situ hybridization for HER2 assay in primary invasive breast cancer. Methods Fluorescence in situ hybridization (FISH) and silver-enhanced in situ hybridization (SISH) for HER2 amplification were performed using tissue microarray. Both methods were used in 257 consecutive primary breast cancers. Results HER2 amplification was observed in 62 (23.1%) of 257 breast cancers based on silver-enhanced in situ hybridization. Of the 257 breast cancers measured using both methods, the results of the two methods were consistent in 248 (concordance: 96.5%; kappa = 0.903). When we compared HER2 amplification in the primary tumor with the metastatic lymph nodes of the same patients, HER2 amplification was observed in nine cases (14.0%) out of 64 cases in which HER2 was not amplified in the primary tumors. In contrast, HER2 status was completely preserved in metastatic lymph nodes showing HER2 amplification in the primary tumor. Conclusions These results indicate that silver-enhanced in situ hybridization can be a feasible alternative to FISH in the clinical setting. In node-positive breast cancer, confirmation of the HER2 status of the metastatic lymph nodes appears to be mandatory, regardless of the HER2 status of the primary tumors. Disclosure All authors have declared no conflicts of interest.