Questions about XY Wen et al. entitled BMatrix metalloproteinase 2 expression and survival of patients with osteosarcoma: a meta-analysis^

XY Wen et al. published an article entitled "Matrix metalloproteinase 2 expression and survival of patients with osteosarcoma: a meta-analysis" in Tumor Biology last year. The investigators demonstrated that high MMP2 expression was associated with poor prognosis in osteosarcoma. After reading these articles, we have some questions about the data extraction and processing in the meta-analysis.