Serum samples should not be used to assess circulating matrix metalloproteinase‐9 levels as a prognostic marker of disease

Abstract

Dear Sir, Ruokolainen et al. have suggested recently that pretreatment serum matrix metalloproteinase (MMP)-9 levels could be of prognostic value in patients with head and neck squamous cell carcinoma. In addition, they have found that patients with high serum levels of MMP-9 had a 2-fold risk of dying compared with patients with low serum MMP-9 levels. There is evidence, however, indicating that these conclusions based on serum MMP-9 measurements may be limited by methodological issues. Importantly, measurement of MMP-9 levels in serum have been reported as artificially high compared with the results obtained from plasma samples. In addition, although a high correlation has been described between MMP9 levels in plasma separated from blood samples drawn into tubes with different anticoagulants, no correlation exists between MMP-9 levels in serum and in plasma. In summary, pre-analytical conditions and other methodological issues are of major importance when assessing MMP in clinical samples. Therefore, we believe that serum samples should not be used to assess circulating matrix metalloproteinase-9 levels as a prognostic marker of disease.