Local Recurrence and Oncological Outcomes After Transanal Total Mesorectal Excision With Intersphincteric Resection for Lower Rectal Cancer: A Nationwide Multicenter Cohort Study (Ta‐Ta‐Mi Study)

ABSTRACT Aim Transanal total mesorectal excision (TaTME) combined with intersphincteric resection (ISR) has emerged as a sphincter‐preserving surgical option for very low rectal cancer. However, multicenter data evaluating oncological outcomes and risk factors for local recurrence (LR) following TaTME with ISR remain limited. This study aimed to evaluate oncological outcomes and identify risk factors for LR in patients undergoing TaTME with ISR. Methods This multicenter retrospective cohort study included patients who underwent TaTME with ISR for lower rectal cancer at 26 institutions participating in the Japan Society for Laparoscopic Colorectal Surgery. Oncological outcomes and clinicopathological factors associated with LR were analyzed. Multivariable analysis was performed to identify independent risk factors for LR. Results A total of 224 patients were included. The 3‐year LR, recurrence‐free survival (RFS), and overall survival (OS) rates were 7.3%, 79.5%, and 98.1%, respectively. Multivariable analysis identified circumferential resection margin (CRM)/radial margin (RM) positivity as the key independent risk factor for LR. In contrast, pathological features, including histopathological classification, lymphatic invasion, vascular invasion, perineural invasion, and tumor budding, reflected tumor biological aggressiveness rather than surgical performance. A biological aggressiveness score demonstrated a stepwise increase in LR risk according to the number of adverse pathological factors. Conclusion TaTME combined with ISR is a feasible sphincter‐preserving option for lower rectal cancer, with acceptable oncological outcomes in a nationwide multicenter cohort. Both surgical factors, particularly margin status, and tumor biological characteristics may contribute to LR risk. Careful margin assessment and close postoperative surveillance are essential for optimizing oncological outcomes.