PDCD4 and metastatic malignant neoplasm: Among the seven members of the miR-17~92 cluster, the guide strand miR-17-5p is predominantly responsible for promoting migration and invasion of metastatic cancer cells, targeting the mRNAs of tumor suppressor genes, such as PDCD4 (programmed cell death 4) and PTEN (phosphatase and tensin homolog) [14].