To test this possibility, a clonogenic survival analysis in response to various doses of irradiation was performed using various breast cancer cell lines, including MCF7 and T47D (HR+/HER2−), MDA-MB231 (HR−/HER2−), BT474 (HR+/HER2+), and SKBR3 (HR−/HER2+). This evidence concerns the gene HR and breast cancer.