ESTRO 2025 - Abstract Book

S1160

Clinical – Lower GI

ESTRO 2025

Median follow-up was 27 months. Patient and tumor characteristics are shown in table 1. The more represented TNM stage was T3N0-2M0 (up to 71%). Median time to re-evaluation was 2.5 months. 38,8% of patients underwent W&W, while 61,2% surgery. Complete response was achieved in 41.2% overall; 34.6% cCR at re-evaluation, who then followed W&W protocol, and another 6.6% achieved pCR in the surgery group. PR was recorded in 55.9% of cases, and 56% of patients avoided permanent colostomy. Local tumor regrowth occurred in 8% overall, while 23% developed distant metastases. At the last follow-up, 71.3% of patients were alive and disease-free, and only 5 patients died in relation to their cancer. Median LC, metastasis-free survival (MFS), and OS were not reached, but the median DFS was 62 months. LC at 24 months was 83.6%, and PFS at 12 months was 95%. In the univariate analysis, lower tumor location correlated with higher local recurrence (p=0.005) and a trend toward worse DFS (p=0.08). Longer time until re-evaluation correlated with higher cCR rates and W&W (p=0.008). Greater response at re-evaluation was linked to better LC, with the exception of cCR, who followed W&W protocol and this was found to be associated with more LR (p=0,006) and a trend toward worse DFS. However, W&W by tumor-board decision vs. patient’s own decision correlated with improved LC, DFS, and DMFS (all p=0.000) and OS (p=0.013). Local regrowth was associated with more distant metastases (p=0,001) and worse PFS (p=0.000). LC and DFS were both associated with improved OS (p=0.016, p=0.000). Regarding toxicity, 80% of patients had acute RT-related toxicity, 74,3% were grade 1. 2,8% had grade 3 diarrhea that was easily managed. Only 7,4% had late toxicities, mostly intermittent tenesmus. Conclusion: TNT and dose-escalated radiotherapy represent a safe and effective approach, resulting in an increased rate of complete responses. The W&W approach, particularly when guided by tumor-board decisions, represents an interesting option yet to be deeply explored. References: Hernando-Requejo O, López M, Cubillo A, Rodriguez A, Ciervide R, Valero J, Sánchez E, Garcia-Aranda M, Rodriguez J, Potdevin G, Rubio C. Complete pathological responses in locally advanced rectal cancer after preoperative IMRT and integrated-boost chemoradiation. Strahlenther Onkol. 2014 Jun;190(6):515-20. doi: 10.1007/s00066-014-0650-0. Epub 2014 Apr 9. PMID: 24715243. Cerdan-Santacruz C, São Julião GP, Vailati BB, Corbi L, Habr-Gama A, Perez RO. Watch and Wait Approach for Rectal Cancer. J Clin Med. 2023 Apr 14;12(8):2873. doi: 10.3390/jcm12082873. PMID: 37109210; PMCID: PMC10143332. Keywords: TNT, escalated-dose, organ-preservation