3383 - Oncological Outcomes of Dose-Escalated Chemoradiotherapy vs. Total Neoadjuvant Therapy in Locally Advanced Rectal Cancer: A Retrospective Analysis

02:30pm - 03:45pm PT

Hall F

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POSTER

Presenter(s)

Abdullah Alswilem, MBBS - King Saud University Medical City, Riyadh, Riyadh

A. M. Alswilem¹, K. K. Hassan^1,2, N. Almazrou¹, S. Aljabab^1,3, Y. M. Alayed^1,3, and A. A. Alsuhaibani¹; ¹Oncology Center, Medical City, King Saud University, Riyadh, Saudi Arabia, Riyadh, Saudi Arabia, ²Kasr Al-Ainy Center of Clinical Oncology (NEMROCK), Cairo University, Cairo, Egypt, Cairo, Egypt, ³Radiation Oncology Unit, College of Medicine, King Saud University, Riyadh, Saudi Arabia, Riyadh, Saudi Arabia

Purpose/Objective(s):

To compare oncological outcomes between dose-escalated long-course chemoradiotherapy (LCCRT) and total neoadjuvant therapy (TNT) in locally advanced rectal cancer (LARC).

Materials/Methods:

This retrospective cohort study analyzed 150 LARC patients treated between 2016 and 2022. All patients underwent curative-intent surgery, with or without adjuvant chemotherapy. Patients were divided into two groups: (1) TNT (70%), which included neoadjuvant chemotherapy (NACT) administered either before or after LCCRT (55 Gy/25 fractions) or short-course radiotherapy (SCRT 25 Gy/5 fractions), and (2) dose-escalated LCCRT (30%; 55 Gy/25 fractions). The primary endpoint was pathological complete response (pCR), while secondary endpoints included radiological complete response (rCR), local recurrence rate (LRR), distant metastasis-free survival (DMFS), disease-free survival (DFS), and overall survival (OS). Kaplan-Meier and Cox models were used for survival analysis.

Results:

At a median follow-up of 53 months, 76% of patients had Stage 3 disease and 16.7% had synchronous metastases. Tumor locations were lower (30%), mid (45%), and upper (25%) rectum. Positive circumferential resection margin (CRM) and extramural vascular invasion (EMVI) were observed in 58% and 29% of patients, respectively. Clinical features, including CRM involvement, nodal status, and lateral pelvic lymph node spread, were comparable across all three groups (P > 0.05). However, lower rectal tumors were more frequent in LCCRT arm (P = 0.0124), while positive EMVI was more prevalent in SCRT + NACT arm of TNT (P = 0.0031). The overall pCR rate was 25%, with LCCRT achieving 28%—comparable to TNT (LCCRT+NACT: 28%, SCRT+NACT: 21%; P = 0.20). The overall rCR rate was 18% with no significant difference between groups (P = 0.28); however, it showed a moderate correlation with pathological response. Regarding surgical outcomes, although 75% of tumors originated in the lower to mid rectum, only 18% of patients required abdominoperineal resection with permanent colostomy, while 32% were eligible for successful ultra-low anterior resection due to significant tumor downstaging. Two- and five-year survival outcomes were as follows: LRR (5.5% and 7.8%), DMFS (88% and 78.6%), DFS (75% and 71%), and OS (91% and 80%), respectively. LCCRT was non-inferior to TNT regarding LRR (P = 0.20), DMFS (P = 0.70), DFS (P = 0.70), and OS (P = 0.40). Worse DFS (P < 0.05) was associated with elevated CEA, EMVI, and ECOG 2, while negative CRM and early-stage tumors predicted better outcomes. Grade 3 toxicities were similar across groups, ranging from 4% to 9%.

Conclusion:

Dose-escalated LCCRT achieved oncological outcomes comparable to TNT, supporting its use as an alternative for patients ineligible for TNT. Further prospective trials are needed to validate these findings.