TP53 and breast cancer: However, of these seven signatures, only signatures 3 and signature 5 are significantly increased in p53 defective compared to WT p53 breast cancers (Figure 6—figure supplement 1B); COSMIC signature 3 is defined by larger deletion mutations (>3 bp) with microhomology at break junctions, consistent with expected RAD52 and POLθ mutation spectra.