Stroma contains extracellular matrix components such as proteoglycans and glycosaminoglycans which are highly negatively charged, largely due to sulfated regions, and bind growth factors and cytokines, acting as a reservoir of these cytokines.[5] In tumors, cancer cells secrete matrix degrading enzymes, such as matrix metalloproteinases (MMPs) that, once cleaved and activated, degrade the matrix, thereby releasing growth factors that signal for the growth of cancer cells.[11] MMPs also degrade ECM to provide space for vasculature to grow to the tumor, for the tumor cells to migrate, and for the tumor to continue to proliferate.[3]