MMP9 and osteosarcoma: Interestingly, an investigation into the role played by MMPs in human osteosarcoma cell lines, xenografts and biopsies found low detectable amounts of MMP‐9 in the U2OS cell line only and MMP‐9 mRNA was below the level of detection in the xenografts, whereas MMP‐9 was not only found in 11/12 biopsies, but was present with very high expression in 5 of those 11 biopsies.3