PLK1 and cancer: The gene expression data from patients with MPNST and benign tumors suggest that the drug targets PLK1 and RRM1, as well as the RRM1 activator RRM2, are upregulated in malignant tumors and that the level of aggressiveness, as indicated by patient survival, is directly associated with the gene expression levels, especially for RRM2 (Fig. 4C–F).