Finally, using an aggressive triple negative breast cancer model that is BRCA1 wildtype, we show that protons combined with PARP inhibition significantly delayed tumor growth (Fig. 6), supporting the in vitro studies indicating that the combination of protons and PARP inhibition generates more cell kill and persistent DNA damage than photons + PARPi, photons alone or protons alone. Here, PARP1 is linked to triple-negative breast carcinoma.