Accumulating evidence indicates that miR-21 is involved in the pathogenesis and progression of cancer, including cell proliferation, migration, invasion, metastasis, and apoptosis, by targeting PTEN, PDCD4, TIMP3, and RHOB [9–12] or by playing important roles in signaling pathways such as, RAS/MEK/ERK, PTEN/PI-3 K/AKT, and Wnt/β-catenin [13, 14]. This evidence concerns the gene PTEN and cancer.