This international multicentre retrospective cohort study aims to research anastomotic leakage after colon cancer resection and has two main objectives:

1. To identify predictive factors associated with 90-day mortality and 90-day Clavien-Dindo grade 4-5 complications amongst patients who developed AL following colon cancer resection and to develop and validate a prediction model for predicting 90-day mortality as well as the co-primary composite endpoint Clavien-Dindo grade 4-5 complications.
2. To explore and compare the effectiveness of various treatment strategies for AL following colon cancer resection, considering patient, tumour, resection and leakage characteristics.

Inclusion criteria:

• Aged 18 years or older;
• Surgical resection for primary colon cancer (cT1-4b, N0-2, M0-1) with formation of a primary colonic anastomosis and with or without diverting stoma;
• Postoperative AL defined as: "any clinical, radiological or intraoperative signs of disrupted integrity of the anastomosis. This also includes suspected leaks with any degree of extraluminal air or fluid on CT, perianastomotic abscess, purulent peritonitis without clear anastomotic defect, or any other suspicious condition in which there is no ultimate macroscopic proof of disrupted anastomosis."
• Regarding the type of colon cancer resection, the following patients will also fulfil the inclusion criteria: patients who underwent cytoreductive surgery (CRS) simultaneous with resection of the primary colon cancer with or without hyperthermic intraperitoneal chemotherapy (HIPEC), simultaneous ablations/resections of metastasis, multivisceral resection, emergency resection, patients diagnosed with perforated disease/peritumoral abscess or fistula, and acute obstructions.

Exclusion criteria:

• Surgical resection for benign colon disease;
• Recurrent colon cancer resection;
• Any primary colon malignancy other than adenocarcinoma (e.g. neuroendocrine tumour, gastrointestinal stromal tumour);
• Any clinical condition that does not fulfil the broad definition of AL as used in this study (e.g. only free air on CT that is considered to be compatible with an appropriate postoperative day in the absence of any other clinical signs related to a potential anastomotic leakage)

Adult patients who developed AL after surgical resection with formation of primary anastomosis for colon cancer (cT1-4bN0-2M0-1).

Data may be available upon reasonable request. Only collaborators with appropriate qualifications and pertinent research inquiries are eligible to request access to the data. The principal investigators of the TENTACLE - Colon study will assess the relevance and appropriateness of the request and their verdict is decisive. If data will be transferred, it will solely be conducted under the appropriate ethical and data transfer agreement.