PDCD4 and neoplasm: Recent studies indicated that several tumor suppressors including phosphatase and tensin homolog deleted on chromosome ten (PTEN) [4], tumor suppressor gene tropomyosin 1 [5], programmed cell death 4 [6], [7], maspin [8], and matrix metalloproteinases inhibitors RECK and TIMP3 [9] were targets of miR-21, suggesting that miR-21 is an important oncogenic miRNA which is closely related to tumor growth and metastasis.