To further understand the role played by the RRM2 gene in the whole biological behavior of tumors, we performed a pan-cancer analysis by the combination of TCGA and GTEx data, which showed that RRM2 was generally highly expressed in tumors of epithelial origin, such as THCA, esophageal carcinoma, and breast carcinoma, suggesting that its pro-carcinogenic mechanism is conserved by the cancer species. This evidence concerns the gene RRM2 and breast carcinoma.