Abstract
<title>Abstract</title> <p> <bold>Background.</bold> The sigmoid take-off (STO) is the internationally agreed anatomical landmark to distinguish rectal from sigmoid cancer on MRI. Its systematic application may reclassify tumors previously managed as rectal cancer, reducing unnecessary neoadjuvant therapy, but its validation in large multicenter cohorts is still lacking. The main aim was to assess the reclassification rate and its impact on treatment and oncological outcomes. <bold>Methods.</bold> Multicenter retrospective cohort study (MOLINO) across 12 Spanish tertiary colorectal units. Patients with rectal adenocarcinoma (stage I-III) who underwent elective curative-intent resection (2017–2023) were included. Preoperative MRI was reviewed by surgeons and radiologists, ambiguous cases were adjudicated by a central radiology panel. Tumors were reclassified as new sigmoid, mid-upper rectum or lower rectum. <bold>Results.</bold> Of 1441 patients, STO was identifiable on MRI in 1411 (97.4%); 328 (22.7%) were reclassified as sigmoid cancer. Neoadjuvant therapy was used in 45.2% of new sigmoid, but was less frequent than rectal cancer (p < 0.001). Postoperative complications (29.9%; p = 0.010), anastomotic leakage (4.5%; p < 0.001), and length of stay (median 5 days; p < 0.001) were lower in the new sigmoid group compared to upper and lower rectum. Despite reduced neoadjuvant exposure, disease-free (p = 0.831) and overall survival (p = 0.653) were comparable between new sigmoid and rectal cancer. <bold>Conclusion.</bold> Systematic STO application reclassified 22.7% of tumors previously managed as rectal cancer as sigmoid cancer, avoiding unnecessary neoadjuvant therapy without compromising perioperative safety or oncological outcomes. These findings support uniform international adoption of the STO in rectal cancer guidelines and multidisciplinary settings. </p>