PDCD4 and non-small cell lung carcinoma: Over-expressed miR-21 can inhibit apoptosis by down-regulating negative regulators, such as programmed cell death 4 (PDCD4), phosphatase and tensin homolog deleted on chromosome ten (PTEN), and activate epidermal growth factor receptor (EGFR) signaling pathway closely related to NSCLC [22–24].