Unrepaired SSBs caused by PARP inhibition, PARP trapping in the DNA by the same drug, and accumulation of DSBs ineffectively managed by error-prone NHEJ are the mechanisms leading to PARPi-mediated killing of HRR-altered cancer cells (Figure 1), which has been demonstrated in this subset of patients with mCRPC [12]. This evidence concerns the gene PARP1 and cancer.