For example, mutations in the tumor suppressors BRCA1 and BRCA2, on one hand, cause enhanced susceptibility to development of breast and ovarian cancers, but on the other hand, tumors in mutant BRCA1 and BRCA2 carriers are extremely sensitive to DNA damaging drugs and to PARP inhibitors that eliminate their only functioning DNA repair arm (Magesa et al., 2000; Yin and Shen, 2008). This evidence concerns the gene PARP1 and ovarian cancer.