Sigmoid take-off as an anatomical landmark for rectal cancer reclassification: impact on multimodal treatment and long-term oncological outcomes—a multicenter retrospective national cohort study (MOLINO study collaborative work)

The sigmoid take-off (STO) is the internationally agreed anatomical landmark to distinguish rectal from sigmoid cancer on magnetic resonance imaging (MRI). Its systematic application may reclassify tumors previously managed as rectal cancer, reducing neoadjuvant exposure, but its validation in large multicenter cohorts is still limited. The main aim of this study was to assess the reclassification rate and its impact on treatment and oncological outcomes. A multicenter retrospective cohort study (MOLINO) was conducted 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, and ambiguous cases were adjudicated by a central radiology panel. Tumors were reclassified as new sigmoid, mid-upper rectum, or lower rectum. 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 tumors, significantly less often than in rectal tumors ( p < 0.001). Postoperative complications (29.9%; p = 0.010), anastomotic leakage (4.8%; p < 0.001), and length of stay (median 5 days; p < 0.001) were lower in the new sigmoid group than in the mid-upper and lower rectum groups. Despite reduced neoadjuvant exposure, disease-free ( p = 0.831), and overall survival ( p = 0.653) were comparable between new sigmoid and the combined rectum group (mid-upper plus lower rectum). Systematic STO application reclassified 22.7% of tumors previously managed as rectal cancer as sigmoid cancer, reducing neoadjuvant exposure without compromising perioperative safety or oncological outcomes. These findings support uniform international adoption of the STO in rectal cancer guidelines and multidisciplinary settings.