Background and purpose: The morbidity of colorectal cancer in China increased year by year. This study aimed to explore the significance of ADAMTS9 protein levels and promoter methylation in colorectal cancer onset and progression. Methods: ADAMTS9 promoter methylation status was detected by methylation specific PCR method in 162 colorectal cancer patients’ peripheral blood DNA samples; Plasmatic ADAMTS9 protein levels was detected by enzyme-linked immunosorbent assay method in 162 colorectal cancer patients and 150 healthy subjects. Results: Compared with healthy people

patients with colorectal cancer had a significant lower ADAMTS9 protein level in plasma [(65.25±9.70)μg vs (50.28±9.66)μg

P0.001]; ADAMTS9 gene promoter methylation was observed in 66 among 162 colorectal cancer patients (40.7%); The plasma level of ADAMTS9 protein in patients with methylated ADAMTS9 gene had significantly reduced (P0.001)

while the plasma level of ADAMTS9 protein in patients with low ADAMTS9 protein had significantly increased (P=0.007); ADAMTS9 methylation is closely related to tumor size (larger

P=0.017) and tumor differentiation degree (P=0.029)

ADAMTS9 protein low expression is closely related to invasion depth (P=0.020)

lymph node metastasis (P=0.019) and Dukes staging (P=0.002).Conclusion: ADAMTS9 protein downregulation induced by DNA promoter methylation may be involved in the pathogenesis

invasion and metastasis

and promote the progression in colorectal cancer.