ObjectiveTo compare the perioperative safety and oncologic efficacy of transanal endoscopic intersphincteric resection (TaE-ISR) and the completely transabdominal approach intersphincteric resection (CTA-ISR) for the treatment of ultra-low rectal cancer. MethodsClinical data of patients who underwent TaE-ISR or CTA-ISR at Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, from June 2022 to June 2023, were retrospectively analyzed. A total of 38 cases of TaE-ISR and 16 cases of CTA-ISR were included. Comparison of surgery-related indexes (including operation time, injury of adjacent organs, protective stoma, and placement of anal tube), postoperative recovery and complications, and oncological results (including positive rate of circumferential resection margin, positive rate of distal resection margin, and number of lymph nodes) were compared between the 2 groups. ResultsThe distance of the lower edge of the tumor from the anal verge was lower in the TaE-ISR group than that in the CTA-ISR group [4.0 (3.4, 4.5) cm vs. 4.9 (4.1, 5.9) cm, P<0.001]. A longer duration of the surgery [(177.18±37.24) min vs (146.25±38.86) min], a higher rate of the anal tube [97.4% (37/38) vs 56.3% (7/16)], a higher rate of protective stoma [94.7% (36/38) vs 12.5% (2/16)], and a higher rate of transanal specimen extraction [92.1% (35/38) vs 0% (0/16)], faster time to first postoperative semi-liquid diet [4 (3, 5) d vs 6 (5, 6) d] were observed in the TaE-ISR group (P<0.05). No adjacent organ injuries occurred in the TaE-ISR group, whereas 2 patients in the CTA-ISR group had intraoperative adjacent organ injuries (0% vs 12.5%), the difference was statistically significant (P=0.026). There was no statistically significant difference between the 2 groups in terms of postoperative hospitalization, postoperative time to first flatus, Clavien-Dindo grading of postoperative complications, the incidence of anastomotic leakage and anastomotic stenosis, distal margin distance, the total number of lymph nodes cleared, and the number of positive lymph nodes (P>0.05). Postoperative specimens in all cases were adequate for distal margins and negative for circumferential margins.ConclusionTaE-ISR and CTA-ISR can both be applied to anus-preserving surgery for ultra-low rectal cancer, but TaE-ISR may be a more reasonable approach than CTA-ISR when the lower edge of the tumor is closer to the anal verge.