Comments on Li H et al. "A systematic review of matrix metalloproteinase 9 as a biomarker of survival in patients with osteosarcoma".

With great interest, we read the article "A systematic review of matrix metalloproteinase 9 as a biomarker of survival in patients with osteosarcoma" (by Li H et al.). This article suggests that high expression of matrix metalloproteinase 9 (MMP-9) is associated with a poor prognosis for patients with osteosarcoma [1]. The result is encouraging. Nevertheless, some flaws existed in this meta-analysis that we would like to point out.