RRM1 and cancer: Previous studies have demonstrated that RRM1, an enzyme indispensable for drug metabolism regulation, plays an important role in chemotherapy resistance in multiple types of cancers.22, 34, 35, 36 Consistently, our quantitative reverse‐transcription polymerase chain reaction and western blot analysis illustrated that RRM1 mRNA and protein expression were significantly upregulated in both GEM‐resistant cell lines.