RRM2 and oropharynx squamous cell carcinoma: Duxbury et al (2005) demonstrated an association of RRM2 overexpression with gemcitabine chemoresistance in pancreatic adenocarcinoma cells: the gemcitabine IC50 was four times higher in RRM2 recombinant than with an empty vector (P<0.05). Goan et al (1999) selected a gemcitabine-resistant cell line KB-GEM (IC50=32 μM) from human oropharyngeal epidermoid carcinoma KB cells (IC50=0.3 μM), and found that RRM2 mRNA (nine-fold) and protein (two-fold) were overexpressed in KB-GEM in comparison with the parental KB cells.