Background There is currently no reliable means to restage rectal cancers after neoadjuvant chemoradiation. There are still no reliable methods to identify patients with pCR before radical surgery. As a result, clinical complete response (cCR), defined as no clinical detectable tumor by physical examination, endoscopic evaluation, and imaging, is designed as a surrogate endpoint for pCR. However, the concordance between cCR and pCR varies from 22% to 96% in different reports, which questions the clinical value of such strategies. Therefore, based on rectal diginal examination, serum CEA, MRI, endoscopy examination, we suggested to add multi-points and full-thickness biopsy technique to further improve the accuracy of cCR.

Inclusion Criteria:

• Adult male and female, between 18 and 80 years old;
• Colonoscopy biopsy pathology confirmed colorectal adenocarcinoma;
• The distance from the lower margin of the tumor to the anal margin ≤12 cm (endoscope) or to the anorectal ring ≤8 cm;
• The hematopoietic functions of heart, lung, liver, kidney and bone marrow meet the requirements of surgery and anesthesia;
• Initial local MRI stage was T2 or T3A or T3B, N0-2, negative for extramural vascular invasion (EMVI), circumferential ential resection margin (CRM), and no peripheral iliac, common iliac, obturator, or abdominal aortic lymph node metastasis;
• CCR patients evaluated after neoadjuvant therapy (no mass or ulcer found on digital rectal examination;Endoscopic examination showed no other changes except flat scar, telangiectasia or pallor of mucosa.MRI or rectal ultrasound showed no residual tumor in the primary site and lymphatic drainage area.Serum carcinoembryonic antigen (CEA) was normal.
• Signing informed consent for surgery.

Exclusion Criteria:

• Previous history of malignant colorectal tumor;

• Patients complicated with intestinal obstruction, intestinal perforation, intestinal bleeding and other patients requiring emergency surgery;

• Unresectable lymph node metastasis;

• Recently diagnosed with other malignant tumors;

• Patients who had participated in or were participating in other clinical trials within 4 weeks prior to enrollment;

• ASA rating ≥IV and/or ECOG physical status score ≥2 points;

• Patients with severe liver and kidney function, cardiopulmonary function, coagulation dysfunction or combined with serious basic diseases cannot tolerate surgery;

• a history of serious mental illness;

  - pregnant or lactating women;

• Those with uncontrolled infection;

• Patients with other clinical or laboratory conditions considered by the investigator should not participate in the study