CHEK1 and breast cancer: Alteration of expression and activation of CHK1 has been identified in a variety of cancer types, including glioblastoma,14 sarcoma,15 breast,16 and colorectal cancer.17 In breast cancer, abnormal expression of CHK1 correlated with advanced tumor behavior.16 However, only few reports have studied activation and phosphorylation status of CHK1 with main focus on pCHK1Ser345.