RRM2 and oral cavity squamous cell carcinoma: Klimaszewska-Wiśniewska A et al. found that RRM2 was highly expressed in lung adenocarcinoma, pancreatic adenocarcinoma, oral squamous cell carcinoma, and cervical cancer [5, 20–23].Our study found that relative levels of RRM2 mRNA expression were up-regulated in breast cancer tissues and cell lines.