The Impact of Malnutrition Risk and Perioperative Complications in Gastrointestinal Cancer Patients Undergoing Elective Major Surgery: A Prospective Observational Multicenter Study

<b>Background/Objectives:</b> The study aimed to characterize perioperative complications and their relationship with nutritional risk in gastrointestinal cancer patients undergoing surgical treatment. <b>Methods:</b> An observational, prospective, and multicenter study was carried out in 469 patients with gastrointestinal malignancies undergoing elective major abdominal surgical procedures in public hospitals throughout Spain. Complications developed during hospitalization and at 30 days after surgery were recorded, and the patients' nutritional status was evaluated using the MUST screening tool. <b>Results:</b> Colorectal and gastric cancer were the most common tumors. Complications during hospitalization occurred in 146 patients (rate 31.1%). Infections accounted for 68.5% of complications, in particular surgical site infections (SSIs), followed by paralytic ileus (40.4%). At 30 days, the complication rate was 9%, with infections as the most common events. In patients with severe nutritional risk at discharge (MUST score ≥ 2), the percentage of patients with complications was 24.7% as compared to 9.2% in patients without complications (<i>p</i> < 0.0001). <b>Conclusions:</b> Clinicians should be aware of the high frequency of SSIs and that complications are higher among patients with severe nutritional risk. These findings emphasize the need for routine nutritional screening and targeted perioperative support in cancer patients undergoing gastrointestinal cancer surgery.