Olaparib(AZD2281, KU0059436) is a selective inhibitor, which can potently inhibit PARP-1 and PARP-2 enzymes with IC50 of 5 nM and 1 nM, respectively. Treatment of these cell lines with 11 different anticancer drugs or with gamma-irradiation showed that AZD2281, a novel and specific PARP inhibitor, caused the strongest differential growth inhibition of BRCA2-deficient versus BRCA2-proficient mammary tumor cells. Synergistic cytotoxicity of AZD2281 and cisplatin against BRCA2-deficient cells but not against BRCA2-proficient control cells.