Purpose: Matrix metalloproteinases are important for matrix turnover in development of metastasis and angiogenesis. Our purpose was to investigate the expression of MMP-9 and itsb prognostic significance in knee osteosarcomas.

Patients: 55 patients with osteosarcoma IIB of the knee area have been studied with respect to the expression of MMP-9 in the surviving tumour cells in the surgical resection specimens

Patients were followed up for at least two and a half years.

Methods: We studied the MMP-9 expression in the resection specimens using immunohistochemistry. The importance of the prognostic factors was assessed using single (log rank test) and multiple variable (Cox regression) analysis. Independence between the factors found significant using the log rank test was studied using the yf test. Significance was set at P< 0.05.

Results: On single variable analysis factors significantly associated with poor survival were high alkaline phosphatase at diagnosis and tumour cells expressing MMP-9 in the resection specimens. The only factor strongly associated with disease free survival was immunohistochemical status of tumour cells for MMP-9 in the resection specimens.

Percentage of necrosis after chemotherapy failed marginally to reach statistical significance.

On Cox regression analysis only MMP-9 remained significant for overall and disease free survival.

Discussion: Once new blood vessels penetrate a microscopic primary tumour or a distant metastasis, the lesions acquire the potential to grow into larger and potentially life threatening tumours. MMP-9 is a factor associated with matrix remodeling during angiogenesis and is also associated with leaky vessels because of its ability to degrade basement membranes. These two properties are very important for tumour growth and development of haematogenous metastases and we believe may explain our findings.