For example, inhibitors of PARP1, which catalyzes the addition of poly- ADP-ribose marks, have been developed for treating tumors with mutations in either BRCA1 or BRCA2 (Lord and Ashworth, 2017) and inhibitors of PARG, which catalyzes the removal of α(1′′–2′) O-glycosidic linkages in PAR chains, are under investigation for a variety of cancers (Slade, 2020). Here, PARP1 is linked to cancer.