SIS-Reinforced vs. Conventional Anastomosis for Mid-to-Low Rectal Cancer: A Multicenter RCT on Anastomotic Leak

Inclusion Criteria-- 1. Age ≤ 85 years old, regardless of gender. 2. Patients with mid - low rectal cancer, where the lower edge of the cancer focus is ≤ 10 cm from the anus and who can undergo rectal anastomosis with a circular stapler (including mid - low and some ultra - low rectal anastomoses). This includes patients after neoadjuvant therapy, patients with insufficient function of important organs such as the heart, liver, and kidneys who can tolerate surgery, and patients after intestinal obstruction stent placement or chemotherapy after intestinal obstruction stent placement. 3. For patients who, after being fully informed by doctors, still clearly refuse neoadjuvant therapy (for advanced rectal cancer) and/or immunotherapy (for MSI - H/dMMR rectal cancer) and request direct surgery, they are generally not included in this study. If a patient insists on enrolling, the operating surgeon must have a second conversation with the patient and/or their family members, and sign in the medical record to confirm the following: The patient is aware of the existence of the neoadjuvant therapy/immunotherapy pathway but refuses the relevant treatment and insists on direct surgery. Only in this case can the patient be allowed to enroll. 4. Patients who received conversion therapy due to distant organ (such as liver, lung) metastasis before surgery and then underwent surgery with primary anastomosis can be included in this study. If organ metastasis is accidentally found during surgery, or if the small intestine or bladder in the pelvic floor is invaded, but the surgeon believes it does not affect rectal anastomosis, the patient does not need to withdraw from the study. 5. The patient or their authorized representative voluntarily signs the informed consent form and can cooperate to complete the follow - up during the trial. Exclusion Criteria-- 1. Patients who, through examination and pre - operative consultation, cannot tolerate routine surgery. 2. Patients who are currently participating in other clinical studies. 3. Since the test device (SIS reinforcement patch) is derived from porcine - sourced materials, out of respect for specific religious beliefs (such as Islam), we do not recommend that subjects whose beliefs prohibit contact with porcine - sourced products participate in this study. We will fully communicate this situation with all potential subjects, and the subjects will make their own decisions based on their personal beliefs and cultural backgrounds. 4. Patients who do not meet the NCCN and the National Health Commission of China's treatment standards for rectal cancer will not be included in this study. For example, patients who should receive neoadjuvant therapy before surgery should preferentially choose neoadjuvant therapy, and MSI - H/dMMR patients are required to undergo immunotherapy first. 5. Due to the possible difficulty in matching the number of patients/omissions with regular patients, patients who require lateral lymph node dissection and those who receive Ta - TME will not be included in this study. 6. Patients who, due to language or intellectual disabilities, cannot understand the content of the trial protocol, cannot complete the follow - up, or for whom the researcher deems there are other situations that are not suitable for enrollment (such as uncontrolled severe underlying diseases, mental illness, etc.).