MMP9 and differentiated thyroid carcinoma: <h4>Objective</h4>The purpose of this study was to investigate the relationship between the expression of matrix metalloproteinase-9 (MMP-9) and pathological indexes in papillary thyroid carcinoma (PTC).<h4>Evidence obtained</h4>The database was searched in PubMed, Embase, CNKI, and Web of Science databases for relevant clinical trials.