CHEK1 and neoplasm: Expression analysis of the 10 core genes in the drug–target network, conducted in normal and tumor tissues, revealed significant differences (p < 0.001) in the expression levels of CCND1, CDK4, CHEK1, CDK2, CDC6, CCNA1, CCNA2, CCNB1, CDKN1B, and MCM5 (Figure 3A).