The purpose of this observational study is to understand the effect of different timing of chemoradiotherapy on overall survival in patients with stage II/III low- and medium-level rectal cancer with or without high-risk factors

Inclusion Criteria:

1. The patient is between 18 and 80 years old;
2. Adenocarcinoma confirmed by pathology;
3. Colonoscopy or imaging examination confirmed that the distance between the lower edge of the tumor and the anal margin is ≤10cm;
4. ECOG score ≤2

(4) Imaging diagnostic analysis was cT1-3NxM0; (for Phase II/III) (5) CT examination of the chest and abdomen and pelvis showed no evidence of metastasis (6) Patients undergoing chemoradiotherapy and surgery

Exclusion Criteria:

1. History of malignant tumors in the past;
2. Diagnosis of simultaneous multiple primary colorectal cancer or other cancers;
3. History of chemotherapy or radiotherapy prior to this trial
4. Those with contraindications to laparoscopic surgery, such as severe cardiopulmonary insufficiency;
5. Patients with intestinal obstruction, intestinal perforation, intestinal bleeding, etc., requiring emergency surgery;
6. Pregnant or lactating women;
7. Evidence of distant metastases prior to surgery
8. T4b tumors were found to invade the uterus, vagina, bladder, seminal vesicles, prostate, bone, and pelvic plexus

Patients with low- and medium-level rectal cancer treated with chemoradiotherapy and surgery