Stability of matrix metalloproteinase-9 as biological marker in colorectal cancer

Matrix metalloproteinases (MMPs) are believed to be of importance in the growth and spread of colorectal cancer (CRC). MMP-9 level has been suggested as a biological predictor of prognosis in CRC as well as in other types of cancer such as breast and cervical cancer. The purpose of this study was to investigate the stability over time of MMP-9 in cryopreserved plasma, colorectal tumor tissue extract and macroscopically tumor-free colon mucosa tissue extract samples. Plasma and tissue samples were taken from patients at primary CRC surgery and analyzed for MMP-9. Aliquots of samples from the same patients were stored at - 80 °C pending analysis. These aliquots were analyzed using identical methods after storage periods of nine (plasma) and twelve (tissue) years. No significant difference in plasma MMP-9 concentration was seen between baseline samples and those after 9 years of cryopreservation (median values 9.9 and 9.7 ng/mL, respectively; p > 0.05). MMP-9 levels in the tumor-free tissue extracts had increased to baseline (median values 7.1 and 8.1 ng/mL, respectively; p < 0.01). MMP-9 levels in the tumor tissue extracts had also increased significantly (median values 89.9 and 133.5 ng/mL, respectively; p < 0.01). We have demonstrated that MMP-9 levels in frozen citrated plasma are stable if stored at - 80 °C, whereas MMP-9 levels in extracts from tumor tissue and tumor-free intestinal mucosa appear to increase with time. We conclude that MMP-9 levels in cryopreserved plasma may be considered stable over time and are thus suitable for comparison purposes in consecutive series.