RRM1 and neoplasm: Increased RRM1 and RRM2 activity was identified in highly metastatic tumour cells (Schallreuter et al, 1992), whereas overexpression of RRM2 in human oral carcinoma cells was shown to be associated with increased invasive potential (Zhou et al, 1998), probably through NF-κB and MMP-9 (Duxbury and Whang, 2007).