Of more than one million global cases of breast cancer diagnosed each year, a high percentage are characterized as triple-negative, lacking the oestrogen, progesterone and Her2/neu receptors. The incidence exceeds the incidence of malignancies like CML by far. Lack of effective therapies, younger age at onset and early metastatic spread have contributed to the poor prognosis and outcomes associated with these malignancies. Here, we investigate the ability of the PI3 K/AKT inhibitor AEZS 126 to selectively target the triple negative breast cancer (TNBC) cell proliferation and survival in vitro by MTT-assays and FACS-based analysis. Furthermore, the mechanism of cytotoxicity is analysed by FACS-based assays and Western blots. Results AEZS 126 showed good antitumour activity in in vitro models of TNBC as well as in MCF-7 cells. We demonstrated the highly efficient antitumour activity of AEZS 126 in in vitro models of TNBC. Due to the good anti-tumour activity and the expected favourable toxicity profile, AEZS 126 in combination with chemotherapy seems to be a promising candidate for clinical testing in TNBC especially in the basal-like subgroup of TNBC.