RRM2 and hepatocellular carcinoma: The mRNA expressions of all hub genes, namely RRM2, MELK, KIF23, NCAPG, BUB1B, AURKB, CCNB1, KIF20A, CCNA2, TTK, PBK, TOP2A, CDK1, MAD2L1, BIRC5, ASPM, CDCA8, and CENPF, except for KIF11 and DLGAP5, showed a significant increase in HCC compared with normal samples, as revealed by the GEPIA database.