Prognostic utility of fluorescence in situ hybridization for determining HER2 gene amplification in breast cancer

An accurate investigation of the HER2 proto-oncogene is extremely important for the therapy and prognostication of breast cancer. Currently, immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) are standard methods for this purpose. The aim of this study was to detect the expression and amplification of HER2 in paraffin-embedded samples of breast cancer tissue and to investigate the relationship between HER2 amplification and various clinicopathological parameters in advanced breast cancers. We used FISH to examine the HER2 gene amplification and IHC to examine the expression of HER2 protein, estrogen receptor (ER) and progesterone receptor (PR) in 62 advanced breast cancers. HER2 gene amplification was detected by FISH in 12 breast cancers (19%) and HER2 protein expression with a score of 3+ was detected by IHC in 11 (17%). There was a significant correlation between the HER2 gene amplification and HER2 protein overexpression in breast cancers (P<0.0001). However, some mismatching was evident: 3 cases, negative for the HER2 gene, showed a HER2 protein expression score of 3+ and 2 cases, positive for HER2 gene amplification, had HER2 protein expression scores of 0 and 1+ (negative), respectively. ER and PR were expressed in 41 (66%) and 46 (74%) cancers, respectively. No correlation was observed between the HER2 gene amplification and any of the clinicopathological parameters examined, including age, histopathological type, TNM stage, tumor size, lymph node status, relapse and expression of PR. We observed three patterns among the 6 deceased cases: i) triple negativity for HER2, ER and PR, ii) positivity for HER2 gene amplification with a mismatching HER2 protein expression, and iii) positivity for the HER2 gene amplification with a matching HER2 protein expression score of 2+ or 3+. The triple negative cases and HER2 gene amplification positive cases with a mismatching HER2 protein expression had a poor outcome. These results suggest that in breast cancer, the detection of HER2 gene amplification by FISH is desirable compared with the HER2 protein expression determined by IHC. Moreover, triple negativity for HER2, ER and PR is a potentially very important prognostic marker.