The surgical therapeutic effect of stage II-IV CRC patients will be assessed by the plasma mSEPT9 assay, and patients will be followed up by the same assay for recurrence monitoring.

Assessment of surgical therapeutic effect of colorectal cancer (CRC) relies on computer tomography (CT) and serum CEA test. CT cannot be used frequently to monitor the instant change of lesions, while CEA cannot cover all patients due to its low sensitivity. The objective of this study is to assess the performance of the methylated SEPT9 (mSEPT9) in assessing the surgical therapeutic effect of CRC.

This study plans to recruit 50 CRC patients with stage II-IV CRC. Plasma samples before surgery, one day after surgery and seven days after surgery will be collected from each subject. mSEPT9 level will be measured at 3 months, 6 months, 9 months, 12 months, 18 months after surgery and relevant chemotherapy to monitor the possible recurrence of CRC. The mSEPT9 level will be measured by the Epi proColon 2.0 assay. The serum CEA will be measured parallel at the identical time points.

Primary outcomes include the plasma mSEPT9 levels before surgery, one and seven days after surgery.

Secondary outcomes include the serum CEA levels before surgery, one and seven days after surgery. It also includes the size of cancer for each patients, the ratio of patients with mSEPT9 complete response (CR), partial response(PR), progressive disease (PD) and stable disease (SD).

Inclusion Criteria:

• stage II-IV CRC patients planning to perform surgery

Exclusion Criteria:

• stage 0-I CRC patients, patients with history of CRC or other cancers, patients not suitable for surgery, pregnant women, patients younger than 30 or older than 80.

stage II-IV CRC patients planning to performe surgery