To evaluate the role of 53BP1 conferring sensitivity to 5-Fu in breast cancer cells, we established stable cell lines that overexpressing 53BP1 in MDA-MB-231 and stable MCF-7 cell lines with shRNA-mediated knockdown of 53BP1. The transfection efficiency was confirmed by western blot and quantitative reverse-transcription PCR analysis (Figure 2A). The gene discussed is TP53BP1; the disease is breast cancer.