Background and purpose: Aberrant DNA methylation that leads to the inactivation of tumor suppressor genes plays important roles in development and progression of breast cancer. Clinically

related gene methylation is considered to be a promising biomarker for tumor diagnosis and prognosis. This study aimed to investigate the methylation status of Sox17 gene in breast cancer tissue and its corresponding plasma circulating DNA

as well as to investigate its value in breast cancer early diagnosis and prognosis. Methods: The Sox17 gene promoter methylation status was detected by MSP in 86 cases of breast cancer

36 normal breast tissues and its paired plasma DNA

the results were analyzed with corresponding clinical and pathological features. Results: The frequency of Sox17 gene methylation rate among 86 breast cancer tissues was 77.9%(67/86)

and was 61.6%(53/86)in plasma circulating DNA

however

no Sox17 gene methylation was found in normal breast tissues. Sox17 gene promoter methylation in plasma circulating DNA was significantly associated with the methylation status in tumor tissues (r=0.502

P=0.000). In breast cancer tissue specimens

Sox17 methylation status was significantly correlated with tumor stage (χ2=6.18

P=0.041) and lymph node metastasis (χ2=13.54

P=0.001); Sox17 gene methylation rate was significantly correlated with tumor stage (χ2=27.06

P=0.000)

tumor size (χ2=9.65

P=0.007) and lymph node metastasis (χ2=20.80

P=0.000) in plasma samples

and there was no significant difference of Sox17 gene methylation between patient age

histological grade and ER

PR

HER-2/neu status. Conclusion: Sox17 gene promoter methylation plays an important role in the carcinogenesis and development of breast cancer

and may be associated with the prognosis of breast cancer. Furthermore

methylated Sox17 gene may be a useful tumor biomarker in plasma circulating DNA for breast cancer detection and disease monitoring.