For this reason, we tested whether reduced H2afx gene expression would also occur in two cohorts of PARPi-resistant mammary tumours from KB1P and KB2P mice (K14cre;Trp53F/F;Brca1F/Fand K14cre;Trp53F/F;Brca2F/F, respectively), that acquired resistance in vivo following repeated PARPi cycles12,18 (Fig. 1d). This evidence concerns the gene H2AX and breast cancer.