MMP9 and neoplasm: MMP-9 expression was significantly correlated with LNM (OR = 3.92, 95% CI = 2.71-5.65, P = 0.000), tumour size (OR = 1.69, 95% CI = 1.13-2.52, P = 0.011), and TNM stage (OR = 2.95, 95% CI = 2.10-4.13, P = 0.000), but not with gender (OR = 0.90, 95% CI = 0.66-1.22, P = 0.487) and age (OR = 1.36, 95% CI = 0.93-1.98, P = 0.115).<h4>Conclusions</h4>Our meta-analysis showed that MMP-9 was significantly associated with LNM, tumour size, and TNM stage; therefore, MMP-9 may be a reliable prognostic biomarker for patients with PTC.