The aim of this study was to compare the different effects of X-ray and carbon ion irradiation on MDA-MB-231 and MCF-7 breast cancer cell lines in terms of cell proliferation, cell colony formation, cell cycle distribution, DNA damage and cell apoptosis and to investigate the role of the Akt/mTOR/p70S6K signalling pathway in radiosensitisation. This evidence concerns the gene MTOR and breast cancer.