While the genes and downstream pathways targeted by miR-21 remain in large part to be elucidated, the tumor suppressor gene PTEN has been validated as a miR-21 target in hepatocellular cancer [7], cholangiocarcinoma [8], non-small cell lung cancer [28] and recently in cervical cancer [55, 56, 64]. The gene discussed is PTEN; the disease is cholangiocarcinoma.