Meng and colleagues showed that PTEN was repressed by miR-21, one of the most frequently upregulated miRNAs in cancer, in hepatocarcinoma cells, suggesting that the oncogenic potential of miR-21 occurs via the downregulation of PTEN expression (Chan et al., 2005; Meng et al., 2006; Volinia et al., 2006; Meng et al., 2007; Si et al., 2007). Here, PTEN is linked to cancer.