Therapeutic effects and limitations of chemoradiotherapy in advanced lower rectal cancer focusing on T4b

Purpose This study aimed to elucidate the benefits and limitations of preoperative chemoradiotherapy (CRT) in rectal cancer treatment, specifically in T4b rectal cancer. Methods This retrospective cohort study reviewed 1014 consecutive patients with clinical T3/4a/T4b adenocarcinomas of the lower rectum, who underwent total mesorectal excision at the Department of Surgical Oncology of the University of Tokyo Hospital and 22 referral institutions affiliated with the Japanese Study Group for Postoperative Follow-up of Colorectal Cancer. Patients were divided into two cohorts: cohort 1 comprised 298 consecutive patients who underwent CRT followed by radical surgery and cohort 2 comprised 716 consecutive patients who underwent curative surgery without preoperative therapy. We assessed the prognostic differences between the two cohorts, focusing particularly on T stages. Results In T3/4a patients, cohort 1 showed a significantly lower local recurrence rate than cohort 2 (4.8% vs. 9.4%, p =0.024), but not in T4b patients (23.5% vs. 16.0%, p =0.383). In contrast, no significant differences in survival were observed between T3/4a and T4b patients. T4b classification was found to be an independent predictive factor of local recurrence in cohort 1, but not in cohort 2. Conclusion In T4b rectal cancer, preoperative CRT demonstrated a limited benefit for local control and survival. In cases of suspected T4b rectal tumors, additional therapies such as induction chemotherapy to conventional CRT may contribute to better outcomes.