In this study, we demonstrate that CIC isolated as a CD44+/CD24−/low/ESA+ subset of cells from both human breast cancer cell lines and primary culture of breast cells isolated from patients with fibroadenoma (patient A) and invasive ductal carcinoma (patient B) were more radioresistant than control subsets and that the radiation resistance cohort was characterized by the presence of stem cells surface markers. This evidence concerns the gene CD44 and breast cancer.