Consistent with these findings, a Phase 1 trial in breast cancer reported grade 3 adverse events for breast cancers treated with RT and the PARP inhibitor Veliparib.40 Toxicity issues for the combination of PARPi and RT are also evidenced by the lip epidermal/mucosal reaction observed in our head and neck tumour model (Fig. 5c). Here, PARP1 is linked to breast carcinoma.