Association of the Primary Care Frailty Index with Postoperative Outcomes in Older Patients Undergoing Major Gastrointestinal Oncologic Surgery: A Retrospective Cohort Study. - Costanzi, Andrea; Fazzini, Nicola; Verdi, Lara; Rossi, Paolo Dionigi; Chiarelli, Marco Enoc; Bonfanti, Giulia; Aseni, Paolo (Journal of Clinical Medicine, 2026)