PARP1 and breast cancer: As expected, PARP1 expression, DNA damage signaling, and the base excision repair pathway (a DNA repair pathway closely associated with PARP1 function) were significantly upregulated in BRCA-mutant breast cancers compared to BRCA-wildtype cases (Figure S4A–C), suggesting that genomic instability associated with BRCA mutations may contribute to PARP1 activation.