Identification of Patients with Locally Advanced Rectal Cancer in Whom Preoperative Radiotherapy Can Be Omitted: A Multicenter Retrospective Study at Yokohama Clinical Oncology Group (YCOG1307).

Objectives The present study aimed to identify patients with locally advanced rectal cancer in whom preoperative radiotherapy (RT) can be omitted. Methods This study was a retrospective multi-institutional study for patients with pathological stage II and III rectal cancer who underwent surgery without preoperative therapy between January 2008 and December 2012. Clinicopathological factors were examined by univariate and multivariate analyses to clarify independent risk factors of local recurrence (LR). Results The 5-year cumulative local recurrence rate (LRR) of 815 patients was 11.2%. Independent predictive factors of LR were determined by a multivariate analysis to be a tumor location of <10 cm from the anal verge, a tumor diameter of ≥50 mm, undifferentiated histological type, and advanced T-N substage (T3N+ or T4Nany). In lower rectal cancer located <10 cm from the anal verge (n = 510), the 5-year cumulative LRR of patients without any remaining three factors was 4.4%, with one factor was 13.0%, with two factors was 22.2%, and with all three factors was 41.6%. Conclusions Preoperative RT may be omitted in patients with lower rectal cancer with no risk factors. However, in addition to the present risk factors, we need to further examine the extramural vascular invasion (EMVI) status and circumferential resection margin (CRM) using magnetic resonance imaging (MRI) findings. The trial was registered with UMIN Clinical Trails Registry, number 000006039.