MMP9 and adenoma: Three studies analyzed the difference in MMP-9 expression between primary and recurrent adenomas (Supplemental Table S7), and the results showed a higher expression of MMP-9 in recurrent adenomas at the protein level (OR = 0.09, 95% CI = 0.01–0.53, P = 0.008) and at the RNA level (OR = −3.66, 95% CI = −5.15 to −2.17, P < 0.00001).