TMPRSS4 and breast cancer: In order to analyze the effect of TMPRSS4 down-regulating and up-regulating on normal TMPRSS4 expression in breast cancer, the MDA-MB-468 and MCF-7 breast cancer cell lines were respectively selected to perform the experiments based on the report of Li et al., (2017) where it has been shown that TMPRSS4 is highly expressed in MDA-MB-468 cells and lowly expressed in MFC-7 cell lines.