Disclosed is a matrix metalloproteinase 9 (MMP9) binding protein (e.g. an antibody) comprising an immunoglobulin heavy chain polypeptide, or functional fragment thereof, and an immunoglobulin light chain polypeptide, or functional fragment thereof, wherein the MMP9 binding protein specifically binds MMP9, and wherein the MMP9 binding protein binds an epitope of human MMP9 comprising amino acid residues R162, E111, D113, and I198. Also disclosed is the use of a cell expressing such a binding protein in the manufacture of a medicament for inhibiting MMP9 activity in a subject having a tumour or tumour-associated tissue having MMP9 activity.
