HER-2 gene amplification by fluorescence in situ hybridization (FISH) compared with immunohistochemistry (IHC) in breast cancer: a study of 528 equivocal cases

The concordance rate between fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC) on evaluating HER-2/neu status is still controversial, especially for the IHC 2+/equivocal cases. In this study, we investigated the amplification of HER-2/neu gene by FISH in IHC (2+)/equivocal specimens to clarify the correlation between HER-2/neu and clinicopathologic features of breast cancers. HER-2/neu amplification was determined by FISH on 528 specimens of breast carcinomas with equivocal expression of HER-2/neu protein by IHC detection. 65.5 % of IHC 2+ patients were negative for HER-2/neu amplification, 29.0 % were positive and the remaining was equivocal. A statistically significant inverse association was found between hormone receptor expression and HER-2/neu amplification (P < 0.05). Furthermore, polysomy of CEP17 was detected in 60 % of breast carcinomas. The results highlight the necessity of FISH test for further categorization when breast carcinoma cases are scored 2+ by IHC.