**3.4 Matrix metalloproteinases and their tissue inhibitors**

Matrix metalloproteinases (MMPs) are a diverse class of at least 25 zinc-dependent endopeptidases, which have important physiological applications and have also been implicated in the invasion, progression and metastasis of CRC. Accordingly, MMPs have been implicated as therapeutic targets, diagnostic and prognostic biomarkers. MMP subclasses have been demonstrated in various types of cancer, including breast and melanoma, and therefore are not cancer specific biomarkers [93].
