MKI-1, combined with radiation, reduced colony formation and breast cancer stemness with the activation of Chk2 and caspase-2, suggesting that MKI-1 may have the capacity to inhibit the intrinsic radioresistance of breast cancer cells through modulation of the mitotic DNA damage response, consequently leading to mitotic cell death following irradiation. Here, CHEK2 is linked to breast carcinoma.