ESTRO 36 Abstract Book

S227 ESTRO 36 _______________________________________________________________________________________________

3 Besançon University Hospital J Minjoz, Department of Radiation Oncology, Besançon, France 4 Unicancer Centre Antoine Lacassagne, Radiotherapy, Nice, France 5 Peter MacCallum Cancer Centre, Division of Radiation Oncology, Melbourne, Australia 6 Goethe University Frankfurt, Department of Radiotherapy and Oncology, Frankfurt am Main, Germany Purpose or Objective Optimal timing of surgery after neoadjuvant chemo- radiotherapy (NAD-CRT) is still controversial. Literature data suggest an improvement in pathological complete response (pCR) after prolongation of surgical interval (SI) after NAD-CRT. The aim of this study was to evaluate the effects of SI on pCR in a pooled dataset of locally advancer rectal cancer (LARC) patients (pts) coming from 7 randomized trials. Material and Methods Pts data were extracted from the following LARC trials: Accord 12/0405, EORTC 22921, FFCD 9203, CAO/ARO/AIO- 94, CAO-ARO-AIO-04, INTERACT and TROG 01.04. Inclusion criteria for pts selection were: LARC (clinical tumor stage (cT) 3-4, clinical nodal stage (cN) 0-1-2 and no distant metastases) and NAD-CRT followed by surgery. The SI was calculated from the end of NAD-CRT. Pts were divided into two groups according to median of the surgery time (MST): shorter interval group (SIG) (pts who had surgery before MST) and longer interval group (LIG) (pts who had surgery after MST). The primary outcome was to determine the rate of pCR related to SI. The secondary outcome was to compare post-surgical complications in two groups and the impact of pCR rates on local recurrence (LR), metastases- free survival (MFS) and overall survival (OS). Pearson's Chi- squared test, Kaplan-Meier curves and univariate logistic regression model (uLRM) were used for data analysis. A p- value<=0.05 was considered significant. Results This pooled dataset included 5247 pts; 3078 pts satisfied the inclusion criteria and were analyzed in this study. Recruitment in the period investigated by the study took place as follows: 453 pts from 1993 to 1998, 613 from 1999 to 2003, 1023 from 2004 to 2008 and 996 from 2009 to 2014. 440 (14%) pts had pCR. The cumulative pCR rate rose significantly when time between NAD-CRT and surgery was increased, until reaching a plateau at 16 weeks (Figure 1). MST was 6 weeks (range 1-31, range interquartile 5-7). The SIG and the LIG had 1953 and 1132 pts, respectively. pCR rates were significantly higher in the LIG as compared to the SIG (19% vs 11.6%, p<0.01). cT, cN, surgery procedure and post surgical complications were distributed equally between the two groups. The results of uLRM are summarized in table 1. Finally, considering only the pCR events there was no statistically significant difference in term of LR, MFS and OS between the two groups. Comparing the two groups, considering pCR and no pCR pts, there was no statistically significant difference in term of LR, MFS and OS between them.

Conclusion The results of these pooled analyses confirm that the prolongation of SI after the end of NAD-CRT increased the rate of pCR in LARC pts. The cumulative pCR rate reached a plateau at 16 weeks; moreover longer SI has no impact on post surgical complication rates. No statistically significant difference was observed in term of survival outcomes between the SIG and the LIG in pCR pts. OC-0429 Neoadjuvant chemoradiotherapy or 5x5 Gy followed by chemotherapy in rectal cancer: the RAPIDO trial C. Marijnen 1 , For the cooperative group of the RAPIDO trial 2 1 Leiden University Medical Center LUMC, Department of Radiotherapy, Leiden, The Netherlands Purpose or Objective Current standard for the most locally advanced rectal cancers is preoperative chemoradiotherapy (CRT), and, variably per institution, postoperative adjuvant chemotherapy. Short-course preoperative radiation with delayed surgery induces tumour downstaging in both randomized and observational studies. In the RAPIDO trial, the value of short-term preoperative radiotherapy with 5x5 Gy followed by neoadjuvant chemotherapy is investigated in a randomized fashion. Material and Methods Patients with rectal cancer with high risk features for systemic or local failure on magnetic resonance imaging were eligible. Randomization took place between a standard arm A : long course chemoradiotherapy followed