Therapeutic approaches based on the principle of synthetic lethality are an attractive strategy for cancer treatment. Since DNA repair pathway aberrations are common in tumor cells but are largely absent in normal cells, agents that target DNA repair-deficient cells may have a clinically exploitable therapeutic window. Some chemotherapeutic agents, such as platinum-based therapy, take advantage of this principle, but their overall toxicity is still significant. PARP inhibitors, on the other hand, were developed to specifically target homologous recombination (HR) deficient cancer cells and have minimal effect on normal cells.