MMP9 and neoplasm: In particular, miR-21 targets reversion inducing cysteine rich protein with Kazal motifs (RECK) gene and promotes cell invasion and metastasis through the control of matrix metalloproteinase 9 (MMP-9) or interacts and downregulates phosphatase and tensin homolog (PTEN) and programmed cell death (PDCD4), favoring apoptosis inhibition and tumor progression.