Expression of HER2 and the coamplified genes GRB7 and MLN64 in human breast cancer:: Quantitative real-time reverse transcription-PCR as a diagnostic alternative to immunohistochemistry and fluorescence in situ hybridization

Purpose: Accurate testing of HER2 is centrally important for breast cancer therapy and prognosis. Immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) are current standard testing methods. As a potential alternative for assessment of HER2, we explored quantitative real-time reverse transcription- PCR (RT-PCR), a fast and inexpensive method yielding quantitative results insensitive to interobserver variability and amenable to standardized scoring. Experimental Design: We assessed HER2 status at the DNA, mRNA, and protein levels with FISH, quantitative RT-PCR, and IHC in 136 tumor samples from 85 breast cancer patients. Expression of GRB7 MLN64, and p21, genes coregulated with HER2, was also quantified with quantitative RT-PCR and correlated with the overall survival (OS) and disease-free survival (DFS) individually and in combination with HER2. Results: Twenty-nine percent and 19% of the patients scored HER2 positive with IHC and quantitative RT-PCR, respectively. In 18 of 19 cases, HER2 statuses in tumors and lymph node metastases were identical. HER2 status significantly correlated with DFS when determined by IHC (P < 0.01), quantitative RT-PCR (P < 0.003), but not with FISH (P = 0.09). The combination of HER2 with MLN64, but not with GRB7 or p21, enhanced the prognostic power for the DFS (P < 0.00005) and OS (P < 0.0008). Conclusions: Quantitative RT-PCR seems to be clinically as useful in the assessment of HER2 status as IHC and FISH, yielding comparable correlations of HER2 status with the OS and DFS. Thus, quantitative RT-PCR analysis of HER2 or HER2 plus MLN64 is a promising complement or alternative to current methods for HER2 testing, particularly in laboratories lacking FISH or IHC technology.