Recent studies indicated that several tumor suppressors including phosphatase and tensin homolog deleted on chromosome ten (PTEN) [20], tumor suppressor gene tropomyosin 1 (TPM1) [21], programmed cell death 4 (PDCD4) [22], maspin [23], and matrix metalloproteinases inhibitors RECK and TIMP3 [24] were targets of miR-21, suggesting that miR-21 is an important oncogenic miRNA which is closely related to tumor growth and metastasis. The gene discussed is PDCD4; the disease is neoplasm.