Patients with cT2-4aN0-2M0 mid- or low-rectal cancer received neoadjuvant chemotherapy or combined chemoradiotherapy. Good responders (cT0-1N0) patients received local excision 4-8 weeks after treatment. Pathologically verified ypT0-1 patients are randomized to observation (local excision group) or complementary rectal excision (total mesorectal excision group). The composite end points include 3 year disease-free survival (DFS), overall survival (OS), recurrence, major morbidity and quality of life.

Total mesorectal excision is still the standard surgical treatment of mid-and low advanced rectal cancer after neoadjuvant treatment. This radical procedure inevitably has the risk of major short and long term morbidity and anorectal function impairment. Additionally, abdominal perineal resection(APR) with permanent stoma is still applied to some low rectal cancer patients, even though major response had been achieved after neoadjuvant treatment. Previous studies have proposed "wait and see" strategy in clinical complete response patients. The local recurrence rate is still high due to residue adenocarcinoma lesion.

Local excision is a conservative alternative approach associated with low mortality and morbidity and high quality of life. In this study, the investigators proposed local excision in good responders (cT0-1N0) 4-8 weeks after neoadjuvant treatment. Patients with pathologically verified complete response (ypT0-1cN0) are randomized to observation (local excision group) or complementary rectal excision (total mesorectal excision group). The purpose of this prospective randomized controlled study is to compare local excision versus total mesorectal excision in pathological complete response (ypT0-1cN0) mid- or low-rectal cancer after neoadjuvant therapy.

Inclusion Criteria:

• 1、Willing and able to provide written informed consent. 2、Histological or cytological documentation of adenocarcinoma of the rectum (≤8 cm from the anal verge).

  3、ypT0-1cN0 after neoadjuvant therapy 4、No metastatic disease. 5、Patient is at least 18 years of age. 6、Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. 7、Non complicated primary tumor (obstruction, perforation, bleeding).

Exclusion Criteria:

• 1、T1, T4 tumour or anal sphincter invasion 2、Metastatic disease (M1) 3、Contra indication for radiotherapy and/or fluoropyrimidine use in chemotherapy 4、Current or recent (within 4 weeks prior to starting study treatment) treatment of another investigational drug or participation in another investigational study 5、History of cancer