Subsequent pre-clinical studies in BRCA1 deficient cells (defective in homologous recombination) demonstrated the concept of synthetic lethality [18–20]; later other studies showed that PARP inhibitors are also effective in cells with “BRCAness” phenotype, which is defined as traits that sporadic cancers share with those occurring in BRCA1 mutation carriers, often due to defects in DNA repair. This evidence concerns the gene PARP1 and cancer.