Development of RT-qPCR-based molecular diagnostic assays for therapeutic target selection of breast cancer patients

Abstract

Breast cancer is a significant cause of death in women. Human epidermal growth factor receptor 2 (HER2), estrogen receptor (ER), and progesterone receptor (PR) are important markers of targeted breast cancer treatment. Currently, the combination of fluorescence in situ hybridization (FISH) studies and immunohistochemical (IHC) staining are basic tests used to identify HER2, ER, and PR. If HER2 was found positive the test, Herceptin would be adopted for HER2-targeted treatment of breast cancer. If ER or PR is positive, estrogen inhibitors such as Tamoxifen will be administrated for ER-, PR- targeted cancer therapy. However, the procedures of IHC and FISH are invasive and involve difficulties in continuous observation of the patients’ prognoses. In addition, because neither IHC nor FISH are standardized, test results can be varied depending upon the methods adopted. Therefore, in this study a molecular diagnostic method based on RT-qPCR was developed to determine the expression of HER2, ER, and PR in more standardized manner. The results from this study showed that the HER2 RT-qPCR test developed in this study using patient’s tissues exhibited 93.0% sensitivity and 89.9% specificity. On the other hand, the HR RT-qPCR test which can be used to test ER and PR using patient’s tissues exhibited 80.2% sensitivity and 94.8% specificity. Subsequently, HER2 RT-qPCR was also conducted with blood specimens to examine whether the assay can detect HER2 mRNA expression in blood of breast cancer patients. The results showed that, over-expression of HER2 mRNA was not identified in blood of normal individuals, but identified in 20.1% of breast cancer patients’ blood. In addition, HER2 mRNA was detected simultaneously with any one of EpCAM, CK19, Ki67, or hTERT, which are known circulating tumor cell markers. When the HER2 RT-qPCR results in the blood were compared with the histological HER2 results inconsistence were found, indicating breast cancer cells in the state of solid tumor may change when they are in the circulating blood. Therefore, the administration of Herceptin can be considered for patients who have an over-expressed HER2 mRNA in blood. In summary, the standardized RT-qPCR based HER2 and HR tests would be helpful for treatment of breast cancer patients.