Evaluation of BrightGen HR RT-qDx assay to detect nuclear receptors mRNA overexpression in FFPE breast cancer tissue samples for selection of tamoxifen therapy

Breast cancer is a significant cause of death in women. Estrogen receptor (ER) and progesterone receptor (PR) are important prognostic factors indicating higher recovery rate in the breast cancer patients. Currently, immunohistochemical (IHC) staining is a conventional method to identify expression of ER and PR. If a breast cancer patient expresses ER or PR, a chemotherapy with estrogen inhibitors such as tamoxifen is supposed to be effective. Although IHC staining is a reliable method, it may not a useful method for continuous monitoring of ER and PR expression changes in multiple breast cancer patients. In the present study, we evaluated an alternative method of IHC for detection of ER and PR expression. A quantitative RT-PCR method called 'the BrightGen HR RT-qDx assay' was employed to detect mRNA expression of the nuclear receptors in 199 formalin-fixed paraffin-embedded (FFPE) breast cancer tissue samples. Among the ER/PR positive samples by IHC, 83 were determined positive and 16 were determined negative for the nuclear receptor mRNA by the quantitative RT-PCR method. Among the ER/PR negative samples by IHC, 37 were determined negative and 2 were determined positive by the quantitative RT-PCR method. The overall sensitivity and specificity of the quantitative RT-PCR method were 83.8% and 94.8% (P = 0.0026), respectively. We also optimized the quantitative RT-PCR method by setting up the diagnostic cut-offvalue using the likelihood ratio. The highest likelihood ratio was when the expression levels of the relative nuclear receptor mRNA passed 103.3 at which sensitivity and specificity was highest. These data suggest that BrightGen HR RT-qDx assay could be an alternative method for detection of the prognostic factors of nuclear receptors expressed in breast cancer patients for providing essential information for therapeutic application of tamoxifen.