RRM2 and neoplasm: Representative CD44+/CD24+ and CD44+/CD24-/low cells are displayed in Figure 2B. The high expression of RRM2 protein was significantly correlated with CD44+/CD24-/low, a tumor stem/progenitor cell indicator (Trends p = 0.044), and Ki-67, a proliferation indicator (p = 0.018) (Additional file2: Table S2, and Figure 2C and D).