To explain the synthetic lethality effect of PARP-inhibitors it has to say that PARP1 is involved in NHEJ [131], cancer cells with deficiency in BRCA or HR will thus require PARP1-dependent NHEJ for DSBs repair, and become more vulnerable to apoptosis when PARP1 is inhibited [129] (Fig. 3A). Here, PARP1 is linked to cancer.