Longitudinal Drain-Fluid Proteomics Reveals Procedure-Specific Signatures of Postoperative Leakage after Pancreatic and Colorectal Surgery

Anastomotic leakage is a major complication after gastrointestinal surgery, yet early detection remains limited by nonspecific clinical signs and narrow biomarker panels. Here, we used longitudinal data-independent acquisition proteomics to profile postoperative drain fluid from two surgical cohorts, comprising 33 pancreatic surgery patients with 201 drain-fluid samples and 34 colorectal surgery patients with 143 drain-fluid samples with an observation window of up to 10 days postoperatively. We aimed to define procedure-specific leakage signatures, evaluate established biomarkers across postoperative time, and identify additional candidate markers beyond routinely measured proteins. In pancreatic surgery, established enzyme markers, particularly AMY2A and PNLIP, showed strong early discrimination between leak and non-leak patients, while in colorectal surgery, the same predefined marker strategy performed less consistently. Discovery analysis revealed divergent temporal patterns. Pancreatic leakage was dominated by early (post-operative day (POD) 1-3) enzyme enrichment followed by inflammatory, antimicrobial, oxidative stress, and matrix-remodeling-associated proteins. Colorectal leakage showed strongest divergence around POD3 and was driven largely by reduced abundance of proteins linked to wound healing, including endothelial integrity, extracellular matrix organization, complement regulation, and coagulation balance. From these procedure-specific patterns, PRSS2 and AZU1 were found for pancreatic surgery, and FBLN1 and CDH5 for colorectal surgery, as novel candidate markers for future follow up validation studies establishing their diagnostic potential. Overall, these data show that postoperative leakage follows procedure-specific proteomic trajectories and support drain-fluid proteomics as a framework for biologically informed biomarker discovery beyond routinely measured markers.