TP53 and breast cancer: Here, we found that in breast cancer cells, overexpression of BRCA1 inhibited cell proliferation and induced apoptosis in p53-expressing cell lines, while the effect of BRCA1 was attenuated in p53-null cells, MDA-MB-157 (Figure 2A and 2B) and validated in HCT116p53−/− cells (Supplementary Figure S1A–S1C).