CHEK1 and breast carcinoma: In conclusion, we identified a specific miRNA signature associated with highly proliferative luminal breast carcinomas, the ability of hsa‐miR‐195‐5p to inhibit CHEK1 expression in breast carcinoma in vitro, and the promising potential for pretreatment of a subset of patients with luminal tumors with Chk1 inhibitors to enhance the efficacy of chemotherapy, underscoring the importance of CHEK1 expression in the prognosis and treatment of patients with luminal breast carcinomas.