Multiple putative targets have been revealed for miR-34a to exert its tumor-suppressive role [50], such as period 1 (Per1) in cholangiocarcinoma [51], NOTCH1 in colon cancer stem cells [52], Hepatocyte nuclear factor 4α (HNF4α) in hepatocellular carcinoma [53] and transforming growth factor-β-induced factor 2 (Tgif2) in bone metastasis [54]. The gene discussed is PER1; the disease is cholangiocarcinoma.