MMP9 and neoplasm: Heterologous expression of αvβ6 in a colon cancer cell line that lacks constitutive αvβ6 expression has been shown by us to enhance tumour growth in vitro and in vivo thought to be due, in part, to αvβ6-mediated matrix metalloproteinase-9 (MMP-9) secretion (Agrez et al, 1994, 1999; Niu et al, 1998).