Representative HER2 (red signal) and CEP17 (green signal) copy number detected by FISH and HER2 protein expression detected by IHC. (a) CEP17 gain with nonamplified HER2 in case 34, original magnification ×1000. (b) HER2 negative expression in case 34. (c) HER2 amplification in breast cancer tissue (positive control, original magnification ×1000). (d) HER2 protein expression positive 3+ in breast cancer tissue (positive control, same case as (c)).