ESTRO 2021 Abstract Book

S1043

ESTRO 2021

median follow-up of 56 months, we observed 29 relapses (20.6%). Most of the relapses were local (83%) and accessible to salvage treatment, mainly by abdominoperineal resection (APR) (67%). 5-year LRC, DFS and CSS were 84.4% ± 3.5%, 74.0% ± 4.2% and 96.6% ± 1.7%, respectively. In multivariate analysis, HPV-negative status was associated with worse LRC (HR 6.40 [95% CI, 2.44-16.79]; p < 0.001), DFS (HR 3.34 [95% CI, 1.39-8.03]; p = 0.007) and CSS (HR 9.47 [95% CI, 1.86-48.15]; p = 0.007). Overall treatment time (OTT) longer than 10 weeks was also independently associated with worse LRC (HR 2.13 [95% CI, 1.10-6.35]; p = 0.030) and DFS (HR 2.09 [95% CI, 1.01-4.32]; p = 0.047). Finally, performing pelvic lymph node irradiation was associated with better CSS (HR 0.22 [95% CI, 0.06-0.84]; p =0.027). Conclusion Exclusive RT is a suitable therapeutic option for early-stage SCCA. Nevertheless, a significant proportion of patients relapsed. The quality of RT (pelvic lymph node irradiation and OTT) and HPV status seems to be of particular importance. PO-1264 Predictive factors of pathological response to neoadjuvant chemoradiotherapy in rectal cancer P. trecca 1 , M. Fiore 2 , L.E. Trodella 3 , G. Petrianni 4 , G. D’Ercole 3 , M. Caricato 5 , R. Coppola 5 , S. Ramella 3 1 Campus BioMedico University of Rome, Radiotherapy , Roma, Italy; 2 Campus Bio-Medico University of Rome, Radiotherapy, Roma, Italy; 3 Campus Bio-Medico University of Rome, Radiotherapy , Roma, Italy; 4 Campus Bio- Medico University of Rome, Radiotherapy , Rome, Italy; 5 Campus Bio-Medico University of Rome, Surgery, Roma, Italy Purpose or Objective The aim of this study was to evaluate pathological complete response rate (pCR) and downstaging rate after neoadjuvant chemoradiotherapy (CRT) in relation to chemotherapy intensification, time interval to surgery and specific relevant clinical factors in patients affected by locally advanced rectal cancer (LARC). Materials and Methods We retrospectively analyzed patients with LARC treated with CRT followed by surgery. pCR was defined as the absence of tumor cells in the surgical specimen, both at the primary tumor site and at regional lymph nodes. Downstaging was defined as lower pathologic T stage compared with the pre-treatment clinical T stage. Patients were divided according to chemotherapy regimens concurrent to radiation therapy (one-drug vs two-drugs) and according to the time interval between neoadjuvant CRT and surgery (≤8 weeks vs >8 weeks), such as in relation to gender, age (≤70 years vs >70 years), clinical stage (II vs III) and distance of tumor from anal verge (≤5 cm vs > 5). Logistic regression was used to estimate the independent factors for pCR and downstaging. Results Among 564 patients diagnosed with rectal cancer and treated at our institution from July 2007 through July 2018, 269 patients resulted eligible for this study. Overall, pCR and downstaging rate was 26 percent (70 patients) and 75.4 percent (203 patients), respectively. Univariate analysis indicated that female gender (p=0.01) and time to surgery > 8 weeks (p=0.04) were associated with pCR; age >70 years (p=0.05) and time to surgery > 8 weeks (p=0.002) were correlated to downstaging after neoadjuvant CRT. At multivariate analysis, interval time to surgery > 8 weeks was the only independent factor for both pCR and downstaging (p=0.02; OR: 0.5, CI: 0.27-0.93 and p=0.003; OR: 0.42, CI: 0.24-0.75, respectively). Moreover, logistic regression analysis showed that other variables, such as a double drugs chemotherapy schedule, were not significantly associated with pCR and downstaging. Conclusion This study indicates that, in our population, interval time from CRT to surgery >8 weeks is an independent significant factor for pCR and downstaging. Further prospective studies are needed. Randomized trials are warranted to define the best interval time. PO-1265 Neoadjuvant rectal and Clavien-Dindo scores in Locally Advanced Rectal Cancer M. Montero Feijoo 1 , S. Qian Zhang 2 , J.J. Barambio Buendía 2 , J.L. Dominguez Tristancho 2 , J. Vara Santos 1 , J. Luna Tirado 1 , L. Guzmán Gómez 1 , A. Alayon Afonso 1 , A. Nieto Rivero 1 , M.A. García Castejón 1 , A.M. Martinez Felipe 1 , I. Azinovic 1 1 H. U. Fundación Jiménez Díaz, Radiation Oncology, Madrid, Spain; 2 H. U. Fundación Jiménez Díaz, General and Digestive Tract Surgery, Madrid, Spain Purpose or Objective Finding factors that can predict the behaviour of rectal cancer is a challenge in order to adapt treatments and avoiding toxicities in patients with less aggressive tumours or intensifying them in those with worst prognosis. Neoadjuvant rectal (NAR) score is a not widely used score that aims to predict OS better than pathological response. The objective of this review is to evaluate NAR score in our database of patients with locally advanced rectal cancer (LARC) and an adapted Clavien-Dindo (aCD) score by using a common terminology with surgical toxicity in patients treated with neoadjuvant therapy (NAT). Materials and Methods Between 2014 to 2018 a total of 150 patients with LARC underwent a long-course radiotherapy treatment. We excluded 15 patients with metastatic disease and 3 patients with synchronic tumours (1 prostate, 2 colon) making final analysis in 132 of the remaining patients. The treatment schedule consisted in 45-54Gy preoperative conventionally fractionated RT. All of them were treated with modern radiotherapy techniques (IGRT: 34.1% MLC; 65.9% VMAT). Concomitantly 125/132 patients (94.7%) received 5FU based chemotherapy. Clinical stage was: 8/132 (6.1%) cT2, 108/132 (81.8%) cT3 and 16/132 (12.1%) cT4. In 121/132 (91.7%) were considered cN+ using MRI. Results Mean NAR score for the whole series was 12.8. In 36/132 (27.3%) had a low-NAR score (<8), 67/132 (50.7%) intermediate (8-16) and 29/132 (22%) high score (>16). NAR score related to TRG is shown in Table 1. The