RRM2 and neoplasm: For example, RRM2, one of the subunits of ribonucleotide reductase complex providing precursors indispensable for DNA synthesis (Engström et al., 1985), was reported lowly expressed in EC compared to the EU in another genome-wide microarray study (Zafrakas et al., 2008), while its overexpression would enhance tumor angiogenesis and growth in multiple cancers (Zhang et al., 2009; Rahman et al., 2013).