HER2 status determination using RNA-ISH--a rapid and simple technique showing high correlation with FISH and IHC in 141 cases of breast cancer.

Aims: the assessment of the human epidermic growth factor receptor 2 (HER2) is currently performed in most laboratories using two techniques: Fluorescence in situ hybridisation (FISH) and immunohistochemistry (IHC), and novel methodology is being investigated continuously in the assessment of HER2, such as SISH, CISH, DNA chips, ELISA or real time PCR to make assessment easier, faster or more accurate. RNA-ISH (RNA in Situ Hybridisation) is a new technique designed to detect mRNA expression levels, conducted by light microscope without the need for counting or grading systems in a total processing time of 4 hours. This study aims to determine if RNA-ISH is a viable and effective technique and a possible alternative to the currently used techniques by analysing and comparing genetic amplification (FISH) and protein levels (IHC) with mRNA over-expression (RNA-ISH) in 141 cases of breast cancer.

Results: This study demonstrated a 96.5% concordance between over-expression of HER2 as determined by RNA-ISH and gene amplification as determined by FISH. The relationship between RNA-ISH-evaluated and IHC-evaluated over-expression was equally well reflected with a 95.2% concordance. Importantly, a considerable reduction in processing and evaluation time was achieved of only 4 hours.

Conclusions: We conclude that the probe developed for RNA-ISH represents a viable, effective possible alternative to FISH and IHC for analysing HER2 status in primary breast tumours.