PTEN and central nervous system cancer: MiRNA-21 exerts its oncogenic function in gliomas through its post-transcriptional targets and downstream signal pathways: PDCD4, phosphatase and tensin homolog (PTEN), tumour protein 63 (TP63), tropomyosin 1 (TPM1), and tissue inhibitor of metalloproteases 3 (TIMP3) [47].