Inclusion Criteria:  age at enrollment is ≥ 18 and ≤ 75 years ECOG PS 0-1 histologically confirmed left-sided colon and rectal carcinoma synchronous para-aortic lymph node metastases confirmed by PET-CT, and located below the level of renal veins and above the bifurcation of iliac artery patients potential to receive surgery and achieve no evidence of disease (NED) able to tolerate surgery providing written informed consent  Exclusion Criteria:  local invasion or distant metastasis other than para-aoritc lymph nodes history of other malignant tumor coupled with severe systematic diseases (recent myocardial infarction, cardiomyopathy, or acute pulmonary infection) emergency surgery