Association of the Primary Care Frailty Index with Postoperative Outcomes in Older Patients Undergoing Major Gastrointestinal Oncologic Surgery: A Retrospective Cohort Study

Background/Objectives: Frailty is increasingly recognized as a major determinant of postoperative outcomes in older patients undergoing oncologic surgery. The Primary Care Frailty Index (PC-FI), a deficit accumulation-based instrument derived from routinely available clinical information, has recently been proposed as a practical frailty assessment tool. However, evidence supporting its application in gastrointestinal surgical oncology remains limited. Methods: We conducted a retrospective cohort study including patients aged ≥65 years who underwent elective major colorectal or gastric cancer surgery between January 2022 and October 2025 at a tertiary Italian hospital. Patients with a PC-FI > 0.07 were included and categorized as having mild (0.07–0.13) or moderate-to-severe frailty (≥0.14). Postoperative outcomes included the Comprehensive Complication Index (CCI), Clavien–Dindo classification, and length of hospital stay. Receiver operating characteristic (ROC) analysis was performed to compare the discriminative performance of PC-FI, ASA classification, and the ACS Surgical Risk Calculator. Results: Ninety-two patients met the inclusion criteria. Patients with moderate-to-severe frailty were significantly older and had higher ASA class, Charlson Comorbidity Index, and ACS morbidity estimates than mildly frail patients. They also experienced a greater postoperative complication burden (mean CCI 25.96 vs. 16.40, p = 0.02) and longer hospital stay (9.89 vs. 7.43 days, p = 0.01). ROC analysis demonstrated modest discriminative performance for PC-FI (AUC 0.63), comparable to ASA classification (AUC 0.68) and the ACS morbidity score (AUC 0.70), without statistically significant differences among the three instruments. Conclusions: Higher PC-FI scores were associated with increased postoperative morbidity and prolonged recovery following major gastrointestinal oncologic surgery. Although its discriminative performance was modest and does not support its use as a stand-alone risk prediction tool, the PC-FI may represent a simple first-line frailty screening instrument to identify older patients who could benefit from comprehensive multidisciplinary perioperative assessment.