1. Study protocol

Before surgery, the patients’ nutritional status was assessed by dedicated dietologists using the Malnutrition Universal Screening Tool (MUST) [¹⁵]. MUST is a 5-step screening tool to identify adults who are malnourished or at risk of malnutrition. The 5 steps include measuring height and weight to get a body mass index (BMI), noting percentage of unplanned weight loss, establishing acute disease effect; then scores of the 3 previous steps must be added to calculate the overall risk of malnutrition and a specific care plan must be developed (Fig. S1).

All of the patients received immune-enhancing enteral nutrition containing arginine, nucleotides and polyunsaturated fatty acids combined in a ready-to-drink-serving (Impact^® Oral; Nestlé, Vevey, Switzerland) based on their score. One serving of this product (237 mL) contains 4.3 g of arginine, 430 mg nucleotides and 1.2 g eicosapentaenoic/docosahexaenoic omega-3 fatty acids, that are considered to be important components of immunonutrition. This product is commonly prescribed by dieticians and also recommended by international guidelines including ESPEN guidelines.

Patients with MUST scores of 0 or 1 (low or medium nutritional risk) received 2 servings per day for 5–7 days before surgery, while patients with MUST scores of 2 received 2 servings per day for 10 days before, based on the protocol developed and validated in our hospital for colorectal oncological surgery in accordance with a systemic review of high-risk surgical patients (Fig. 1) [¹⁶].

MUST, Malnutrition Universal Screening Tool.

In early stages (International Federation of Gynecology and Obstetrics [FIGO] stage Ia–c) patients underwent cytoreductive surgery consisting in hysterectomy, bilateral salpingo-oophorectomy, omentectomy, peritoneal staging, pelvic and para-aortic lymphadenectomy; in advanced disease also bowel resection, diaphragm or other peritoneal surface stripping, resection of suspicious and/or enlarged nodes (instead of systematic lymphadenectomy) could be necessary to remove all gross disease for a complete debulking. Single points (1 or 2) were assigned to each surgical procedure performed according to its complexity, in order to calculate the Surgical Complexity Score (SCS) developed by Aletti et al. [¹⁷]. A SCS of 0–3 was considered low, 4–7 moderate and ≥8 high.