CCNA2 and breast cancer: Validation of promoter methylation through Student’s t-test between normal and primary tumor using the UALCAN database revealed that the promoter methylation level of BUB1B and CCNB2 was lower than that of the normal samples in breast cancer, which indicates the higher expression of these hub genes (Figure 7b,d) (p < 0.05) in contrast to that of AURKA, CCNA2 and PBK having a higher promoter methylation level than the normal samples (Figure 7a,c,e) (p < 0.05).