CHEK2 is classified as a moderate-penetrance gene for hereditary breast cancer (BC). In Russia, CHEK2 mutations hold second position in the list of BC-predisposing gene defects after BRCAl, and include CHEK2 1100deIC, de15395, and IVS2+lG>A gene-inactivating alleles. CHEK2-driven breast carcinomas are generally characterized by poor prognosis and low sensitivity to the conventional therapeutic regimens. CHEK2 testing needs to be incorporated into routine clinical practice owing its overt clinical significance.