Risk Factors for Microscopically Non-radical Surgical Resection in Patients With Rectal Cancer Undergoing Neoadjuvant Radiotherapy

Background/Aim: Achieving a microscopically radical (R0) resection is essential in rectal cancer surgery to reduce local recurrence, distant metastases, and improve long-term survival. This retrospective cohort study aimed to identify factors associated with microscopically non-radical (R1) excision in patients undergoing surgery for rectal adenocarcinoma at a Swedish tertiary referral center. Patients and Methods: Patients with rectal adenocarcinoma operated on between January 2015 and December 2020 at Skåne University Hospital, Malmö, were identified through the Swedish Colorectal Cancer Registry and complementary chart review. Clinical, pathological, and perioperative variables were compared between patients with R0 and R1 resections. R1 resection was defined as a circumferential resection margin (CRM) ≤0.1 mm or an involved longitudinal resection margin. Factors associated with R1 status were analyzed using univariable and multivariable logistic regression. Results: Among 348 included patients, 17 of 309 (5.5%) with available resection status had a microscopically non-radical resection (R1), while resection status was missing for 39 patients. Distal tumor location was strongly associated with R1 status: tumors ≤7 cm from the anal verge had an increased risk of non-radical excision [adjusted odds ratio (aOR)=3.77, 95% confidence interval (CI)=1.23-14.2]. Longer operating time was related to R1 resection (median 531 vs. 415 min, p=0.045); however, this association was not retained after adjustment (OR=1.21, 95%CI=0.42-3.58). Advanced pathological T stage (pT3-4) was associated with higher R1 risk (aOR=4.15, 95%CI=1.06-27.7). In contrast, examination of more than 22 lymph nodes was associated with a lower risk of R1 resection (aOR=0.17, 95%CI=0.04-0.56). Conclusion: Distal tumor location and advanced pathological tumor stage are key risk factors for microscopically non-radical resection in rectal cancer, whereas an extensive lymph node yield appears protective. These findings support meticulous preoperative planning and tailored surgical strategies for low rectal tumors to minimize the risk of R1 excision.