Lower preoperative CALLY index indicates worse survival and higher complications in cancer patients undergoing surgery.

• Each unit decrease in CALLY index increases the risk of overall survival failure by 91% (HR: 1.91, p < 0.001).
• Patients with low CALLY index had 88% higher recurrence risk (HR: 1.88, p < 0.001) and 151% higher cancer-specific mortality (HR: 2.51, p < 0.001).
• Major postoperative complications are nearly double with low CALLY levels (OR: 2.07, p = 0.005).

Integrating CALLY index into preoperative assessments may refine risk stratification and improve surgical outcomes.