CEACAM5 and neoplasm: The secondary objectives were to evaluate the association between preoperative carcinoembryonic antigen (CEA) levels and tumor response to neoadjuvant therapy and to explore whether TNT is associated with increased surgical difficulty, using surrogate pathological indicators such as total mesorectal excision (TME) quality, circumferential resection margin (CRM) status, and R0 resection rates.