To evaluate the effectiveness of the gastroscopy, air, and methylene blue (GAM) leak testing in reducing the incidence of postoperative anastomotic complications, especially anastomotic leakage, in patients with colorectal cancer. The primary outcomes included is the incidence of anastomotic complications (mainly anastomotic leak) within 30 days after surgery

Inclusion Criteria:

1. Patients diagnosed with colorectal cancer by pathology and scheduled for surgical treatment who meet the surgical indications.
2. Aged between 18 and 85 years.
3. American Society of Anesthesiologists (ASA) physical status classification is I - III.
4. The patient or his/her legal representative can understand and sign the informed consent form and is willing to cooperate throughout the study process.

Exclusion Criteria:

1. Patients with preoperatively diagnosed anastomotic leak or other severe abdominal infections.
2. Patients with severe cardiovascular and cerebrovascular diseases (such as recent myocardial infarction, unstable angina pectoris, severe heart failure, acute cerebral infarction, etc.) who cannot tolerate surgery and related tests.
3. Patients with severely impaired liver and kidney function (liver function Child - Pugh classification C or above, creatinine clearance rate < 30 ml/min).
4. Patients with coagulation disorders (such as platelet count < 50×10⁹/L, international normalized ratio (INR) > 1.5, etc.) that cannot be corrected or are receiving anticoagulant therapy that cannot be adjusted.
5. Patients with a history of abdominal radiotherapy or multiple abdominal surgeries and severe abdominal adhesions that may affect the operation and detection procedures.
6. Patients with other malignant tumors who are receiving active anti-tumor treatment such as radiotherapy and chemotherapy.
7. Patients with mental illness or cognitive impairment who cannot cooperate with the study process and follow-up.