To evaluate whether ATM inhibition increases the cytotoxicity of PARP inhibitors, we treated both triple-negative breast cancer cell lines (CAL-51, MDA-MB-231 and MDA-MB-468) and non-triple-negative breast cancer cell lines (MCF-7, T-47D and SK-BR-3) with increasing concentrations of Olaparib (0–10 μM) alone or in combination with 10 μM ATM inhibitor KU55933. Here, ATM is linked to triple-negative breast carcinoma.