Whether patients with stage II colon cancer should receive adjuvant chemotherapy or not is still on debate.MicroRNA(miRNA) is a promising tool. Investigators invented a tool consisting of 6 miRNA(miR-21、miR-20a-5p、miR-103a-3p、miR-106b-5p、miR-143-5p and miR-215) that was effective to identify one should accept adjuvant chemotherapy or not. Here investigators randomly assign patients to be assessed by classical pathological features or the miRNA tool of determining who should accept chemotherapy. Disease free survival and overall survival are the end points of observation.

Investigators randomly assign patients to be assessed by classical pathological features(control group) or the miRNA tool(experimental group). Pathological features include poorly differentiated histology(exclusive of those cancers that are MSI-H),lymphatic/vascular invasion,bowel obstruction and <12 lymph nodes examined.MicroRNA tool contains miRNA of miR-21、miR-20a-5p、miR-103a-3p、miR-106b-5p、miR-143-5p and miR-215. Investigators evaluate these miRNA status of surgical specimens using qRT-PCR and calculate their risk score(risk score =(0.108×status of miR-21-5p)+(0.086×status of miR-20a-5p)+(0.240×status of miR-103a-3p)+(0.095×status of miR-106b-5p)-(0.238×status of miR-143-5p)-(0.237×status of miR-215),low expression status equals 0 and high expression status equals 1). Investigators defined high risk patient if had any pathological features in control group or the score larger than 1 in the experimental group ,the others as low risk patient.The high risk group should receive adjuvant chemotherapy while the low risk group deserve observation. Primary endpoint is the disease free survival and overall survival.

Inclusion Criteria:

• The informed consent has been obtained from the patient.
• With confirmed diagnosis of stage II colon cancer.
• With moderate/good ECOG health rating (PS): 0-1 score.
• The patient receive no anti-cancer treatment before primary surgery.
• The patient receive radical operation for colon cancer with negative margin.

Exclusion Criteria:

• With severe comorbidities, such as cardiovascular disease, chronic obstructive pulmonary disease, diabetes mellitus, and chronic renal dysfunction.
• With bad compliance or contraindication to enrollment.
• Pregnant woman or lactating woman.
• With contraindication to receive adjuvant chemotherapy.