Abstract
PURPOSE: Valid determination of HER2 status is a prerequisite to establish an adequate treatment strategy for breast cancer patients, regardless of the disease stage. The goal of this study was to examine the feasibility of the newly developed silver-enhanced in situ hybridization (SISH) technique as an alternative to fluorescence in situ hybridization (FISH) for HER2 assay in primary invasive breast cancer. METHODS: FISH and 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 a total of 257 breast cancers based on SISH. 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. CONCLUSION: These results indicate that SISH 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.