ESTRO 2025 - Abstract Book

S1276

Clinical – Lower GI

ESTRO 2025

resection margin (CRM), sphincter invasion (SI) and Extramural venous invasion (EMVI)) were collected and analyzed. A subgroup analysis for patients with different Mandard TRGs divided in good responders (TRG1-2) and poor responders (TRG3-5) was performed. Mantel cox test for survival curves comparison and Cox proportional hazards model for multivariate analyses were conducted. Results: The median age was 68 years and the median follow-up of 42 months. Following neoadjuvant CRT the rate of good responder (TRG 1-2) patients was 62%. Regarding the MRI features, a MTI>5mm was registered in 19 patients; a CRM≤1mm, in 31 patients; the presence of SI and of EMVI, in 5 and in 30 patients, respectively. The Mantel-Cox test showed statistical significance in: CRM<1mm vs CRM>1mm for LC (p=0.05) and in MTI>5mm vs MTI<5mm for DFS (p=0.02) (Fig.1).

Particularly, CRM>1mm and CRM<1mm 5-year LC was 92% vs 64%, respectively; MTI>5mm and MTI<5mm 5-year DFS was 75% vs 42%, respectively. At multivariate analysis, we observed a higher risk of local failure and distant metastasis for good responders with MTI>5mm such as for poor responders with presence of EMVI and a CRM≤1mm (Table 1).

Conclusion: Beyond the role of staging and restaging, MRI can identify features in LARC patients that can be used to tailor and personalize patient treatment. In our analysis, MTI, CRM and EVMI were correlated to better LC and DFS rates and hazard ratios.

Keywords: rectal cancer, pathological complete response, MRI