S679
Clinical – Lower GI
ESTRO 2026
Keywords: neoadjuvant chemotherapy, response evaluation
Purpose/Objective: Neoadjuvant chemotherapy (NCT) is gaining
acceptance for the treatment of locally advanced rectal cancer (LARC) without high-risk factors.1-4 The poor responders to chemotherapy carry negative prognostic risks and should be identified early. We evaluated the possibility of early response evaluation to NCT based on MRI in LARCs. Material/Methods: From two consecutive prospective clinical trials: the expanded phase II trial (December 2017 to May 2021, NCT03666442) and the multicenter randomized
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Postinduction Response Evaluation in Total Neoadjuvant Therapy of Rectal Cancer: Who benefits from the TNT? Yu Shen, Tianxiang Jiang, Ziqiang Wang Colorectal Cancer Center, West China Hospital, Chengdu, China Purpose/Objective: Total neoadjuvant therapy (TNT) has improved pathological complete response (pCR) rates for locally advanced rectal cancer (LARC).1-4 The relationship between tumor response after induction chemotherapy (INCT) and ultimate pCR remains undefined. This study aimed to evaluate the association between post-induction (PI) tumor response after INCT and the ultimate treatment response in LARCs undergoing TNT. Material/Methods: This single-center retrospective cohort study (2018 to 2022) included consecutive LARC patients receiving TNT with at least 2 INCT cycles of INCT and underwent MRI at both PI (before radiotherapy) and pre-operative (PO) timepoints. The primary outcome was the pCR rate. MRI tumor regression grade (MR-TRG) and tumor longitudinal length reduction rate (TLLR) were used to evaluate the tumor response at PI. The combination of MR-TRG and DWI was used to determine the presence of MRI complete response (mriCR) at PO. The associations between PI response and PO response, PI response and pathological response were established. A univariate logistic regression model was used to establish associations between PI response and PO response, PI response and pathological response. Results: Among 224 included patients, the pCR rate was 23.2% (52/224). Based on TLLR, 65.6% (147/224) achieved partial response (PR) at PI. Among these, 33.3% (49/147) achieved mriCR at PO and 30.6% (45/147) achieved pCR. In contrast, non-PR patients at PI (77/224, 34.4%) had significantly lower mriCR rate 11.7% (9/77, p<0.001) and pCR rate (7/77, p<0.001). Compared to non-PR patients at PI, PR patients had higher odds of both PO mriCR (OR 3.788, 95%CI 1.740- 8.202, p<0.001) and final pCR (OR 4.412, 95%CI 1.881- 10.347, p<0.001). After a median follow-up of 44 months, good responders at PI, based on both TLLR and MR-TRG, recorded a better recurrence-free survival (RFS) compared with non-PR patients. Conclusion: In conclusion, MRI-based response evaluation after INCT is a powerful and practical tool that identifies
COPEC trial (August 2021 to October 2024, NCT04922853), LARC participants receiving
neoadjuvant CAPOX were included. Three reviewers blinded to the clinicopathologic data independently evaluated the MRI to determine the radiological tumor response at pre-operative evaluation (PE) and mid- term evaluation (ME) using MRI tumor regression grade (MR-TRG), tumor longitudinal length reduction rate (TLLR), and tumor volume reduction rate (TVR). With pathological assessment as reference, the accuracy of these models in identifying poor responders to NCT at PE and ME is evaluated. Results: This study included 648 patients and have two evaluation time points, with 301 participants eligible at ME and 587 eligible at PE. There is a very strong correlation between radiological tumor response at ME and PE (r=.80 for MR-TRG, .87 for TLLR, and .86 for TVR). MRI accurately identified poor responders to NCT, with the highest PPV of .863 for immediate identification at PE and .857 for predictive identification at ME. Conclusion: Tumor response to NCT may have been determined early. Poor responders to NCT benefit little from the prolonged NCT. MRI-based tumor response models are efficient modalities for both immediate and predictive identification of poor responders to NCT, enabling treatment-response-guided strategies. References: 1.Taylor FG, et al: Preoperative high-resolution magnetic resonance imaging can identify good prognosis stage I, II, and III rectal cancer best managed by surgery alone: a prospective, multicenter, European study. Ann Surg 253:711-9, 20112.Bossé D, et al: PROSPECT Eligibility and Clinical Outcomes: Results From the Pan-Canadian Rectal Cancer Consortium. Clin Colorectal Cancer 15:243-9, 20163.Deng X, et al: Neoadjuvant Radiotherapy Versus Surgery Alone for Stage II/III Mid-low Rectal Cancer With or Without High-risk Factors: A Prospective Multicenter Stratified Randomized Trial. Ann Surg 272:1060-1069, 20204.Schrag D, Shi Q, Weiser MR, et al: Preoperative Treatment of Locally Advanced Rectal Cancer. N Engl J Med, 2023
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