MMP9 and neoplasm: TIMP-1 availability should prevent formation of MMP-9 dimers (Goldberg et al, 1992), while we found high levels of the homodimer of MMP-9 (220 kDa, Figure 1) and the heterodimer of MMP-9 and NGAL (135 kDa) (Zeng et al, 1999), indicating that there is unbound MMP-9 left in tumour tissue.