FISH for HER-2/neu in breast cancer: standardization makes the difference!

Overexpression of HER-2/neu oncogene in breast cancer patients is correlated with disease free survival (DFS) and overall survival (OS). The most commonly used methods for the detection of HER-2/neu status are immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH). However, therse is a lot of controversy with regard to the best method. Most of the FISH studies chose arbitrary cut-off levels for positive results (10%) and had no validation.

In order to address these issues, we designed a pilot study of 38 samples with known IHC status representing all 4 categories.

FISH was performed using Vysis Pathvysion probe. For validation, 5 cases of reduction mammoplasty were analyzed using same protocols.

Our results showed significant discordance between FISH and IHC. The rate of discordance was much higher in the 0, 1+, and 2+ categories compared to published literature. This could be due to the lower cut-off rates for positive amplification established by validation in our study (5.7% vs 10%). Our analysis showed that FISH positive and IHC negative patients have a poor prognosis in terms of DFS and OS compared to FISH negative and IHC negative patients. Further, our results also showed that IHC in comparison to FISH has a comparable specificity (98%), but has a very low sensitivity (46%).

Based on these results, we consider FISH to be the gold standard for detecting HER-2/neu status in breast cancer.