S744
Clinical – Lower GI
ESTRO 2026
Digital Poster 4831 Neoadjuvant Radiotherapy in Rectosigmoid Junction Cancer: Comparison with Mid-Low Rectal Tumors Xeila Bernárdez Martínez, Alejandra Margarita Morón Guerrero, María Luisa Vázquez de la Torre, María del Mar Sevillano Capellán, Victor Manuel Muñoz Garzón, Patricia Willisch Santamaría Radiation Oncology, Meixoeiro, Vigo, Spain Purpose/Objective: The role of preoperative radiotherapy in rectosigmoid junction tumors is controversial, as these tumors can be managed either as rectal or colon cancers. To determine whether preoperative radiotherapy provides benefit in these tumors, we analyzed a series of patients with rectosigmoid junction tumors treated with rectal cancer radio-chemotherapy protocols and compared the outcomes with another series of patients with mid- and low-rectal cancer treated with similar protocols during the same time period. Material/Methods: We conducted a single-center retrospective study including 92 patients with rectal cancer treated with neoadjuvant radio-chemotherapy followed by surgery. Patients were classified into two groups according to tumor location, using the peritoneal reflection as the anatomical landmark: rectosigmoid junction tumors (above the reflection) and mid-low rectal tumors (below the reflection). Demographic and clinical variables were collected, including clinical and pathological stage, chemotherapy regimen, local and distant recurrences, pathological complete response (pCR) rate, and overall survival (OS). Toxicities ≥ G2 (hematologic, gastrointestinal, urinary, and cutaneous) were also recorded. Median follow-up was 63 months. A comparative analysis between the two groups was performed. Results: Of the 92 patients, 45 had rectosigmoid junction tumors and 47 had mid-low rectal tumors, with median ages of 68 and 65 years, respectively. Regarding chemotherapy regimen, in rectosigmoid junction tumors, 58 % received conventional chemotherapy, 31 % received total neoadjuvant therapy (TNT), and 11 % did not receive systemic treatment; in mid-low rectal tumors, the corresponding percentages were 79 %, 11 %, and 11 %, respectively. Local recurrences occurred in 2.2 % and 4.3 %, and distant metastases in 8.9 % and 31.9 %. The pCR rate was 26.1 % in rectosigmoid junction tumors and 12.8 % in mid-low rectal tumors. Overall survival was 72.8 %, with a median of 63.2 months; by groups, 77.8 % (median 56.8 months) in rectosigmoid junction tumors and 68.1 % (median 67.1 months) in mid-low rectal tumors. Toxicity ≥ G2 was observed in 56.5 %,
Conclusion: Integration of baseline pathological characteristics, initial MRI features, and MRI-based post-treatment response parameters enhances prognostic stratification in LARC. These findings support personalized treatment decision-making, particularly for high-risk patients who may benefit from therapeutic intensification beyond standard nCRT. References: 1. Marinkovi ć M et al. Performance and Dimensionality of Pretreatment MRI Radiomics in Rectal Carcinoma Chemoradiotherapy Prediction. J. Clin. Med. 2024; 13, 421.2. Marinkovi ć M et al. Exploring novel genetic and hematological predictors of response to neoadjuvant chemoradiotherapy in locally advanced rectal cancer. Front. Genet. 2023; 14:1245594. Acknowledgments: This study was funded by the Horizon Europe STEPUPIORS Project (HORIZON- WIDERA-2021-ACCESS-03, European Commission, Agreement No. 101079217) and the Ministry of Science, Technological Development and Innovation of the Republic of Serbia (Agreement No. 451-03- 136/2025-03/200043). This study is based upon work from COST Action CA23111; www.cost.eu. Keywords: LARC, nCRT, DFI, prognostic biomarkers
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