The goal of this observational multicenter study is to evaluate the safety and feasibility of a single-stapled technique (SST) for colorectal anastomosis and to explore whether this technique is associated with a reduced rate of anastomotic leakage compared with the conventional double-stapled technique (DST).

The study includes adult patients undergoing planned left-sided colorectal resection with colorectal anastomosis, including sigmoid resection, left hemicolectomy, or partial mesorectal excision (PME), for benign or malignant disease.

The main questions it aims to answer are:

What is the rate of anastomotic leakage within 90 days after surgery in patients operated with the single-stapled technique?

Is the single-stapled technique feasible and safe across different surgical approaches (open, laparoscopic, and robot-assisted surgery) in a multicenter setting?

Furthermore, outcomes after single-stapled anastomosis will be compared with a retrospective cohort of patients operated with the conventional double-stapled technique to explore potential differences in anastomotic leakage rates and postoperative complications.

Participants will receive standard surgical care as determined by the treating surgical team. Patients included in the prospective part of the study will undergo colorectal anastomosis using the single-stapled technique as part of routine clinical practice. Data on perioperative variables, postoperative complications (including anastomotic leakage graded according to international consensus definitions), and follow-up outcomes will be collected prospectively using an electronic case report form (eCRF). A retrospective cohort from the same participating centers will be identified through medical record review using identical inclusion criteria.

The results of this study are intended to provide robust multicenter data on the safety and clinical outcomes of the single-stapled technique and to serve as the basis for planning a future randomized controlled multicenter trial.

Inclusion Criteria:

• Age ≥ 18 years.
• Planned (elective) left-sided colorectal resection with creation of a colorectal anastomosis, including: Left hemicolectomy, and/or Sigmoid resection, and/or Partial mesorectal excision (PME).
• Benign or malignant indication.
• Prospective cohort: Ability to provide written informed consent.
• Retrospective cohort: Eligible patients operated during 2023-2025 at participating centers, identified through medical record review, meeting the same surgical inclusion criteria.

Exclusion Criteria:

• Total mesorectal excision (TME) (e.g., low rectal cancer surgery requiring TME).
• Non-left-sided colorectal resections (e.g., right-sided colectomy) or procedures outside the study-defined operations.
• Surgery not involving a colorectal anastomosis (e.g., end colostomy/Hartmann's procedure without anastomosis).
• Emergency/urgent colorectal resection (non-elective surgery).
• Prospective cohort: Inability to provide informed consent.

The study population consists of adult patients (≥18 years) undergoing planned left-sided colorectal resection with construction of a colorectal anastomosis, including left hemicolectomy, sigmoid resection, or partial mesorectal excision, for benign or malignant indications.

Patients are treated as part of routine clinical care at participating centers. The study includes both a retrospective cohort of patients operated during 2023-2025 and a prospective cohort of consecutively included patients undergoing surgery after study initiation. In the prospective cohort, the intent is to perform a single-stapled colorectal anastomosis when technically feasible in all consenting patients.