ESTRO 2020 Abstract book

S627 ESTRO 2020

To evaluate how post-treatment carcinoembryonic antigen (CEA) serum concentration decrease corresponds with the outcome of definitive radiotherapy (RT) or radiochemotherapy (RT-CHT) in primary unresectable rectal cancer patients (pts). Material and Methods Inclusion criteria of this retrospective study were: primary unresectable, locally advanced rectal cancer with histopathological confirmation, RT/RT-CHT as radical treatment and measured CEA post-treatment level. Between 2000 and 2016 145 pts were treated due to unresectable rectal cancer. The aim of the treatment was tumour downsizing allowing further radical surgery. Among them, 71 had pre- and post-treatment CEA and 10 post-treatment CEA measurements, therefore the group of 81 pts (60 men, 21 women) was evaluated in this study. Out of 81 pts: 33 (41%) received RT (accelerated hyperfractionation: 66 Gy in 1.5 Gy fx, twice a day or conventional fractionation 60-66 Gy in 2 Gy fx) and 48 (59%) RT-CHT (54 Gy/1.8 Gy fx +2 cycles of 5-Fu LV). Six to eight weeks after RT or RT-CHT tumor resectability was evaluated again using physical examination and imaging studies. Pts were divided in two groups. (group A): pts with CEA post-treatment decrease or below 5 ng/ml and (group B): pts without post-treatment decrease of CEA or level above 5 ng/ml. Statistical test used were Kaplan-Meyer survival analysis, log rank test and Cox regression model. Results Median follow-up after the end of RT/ RT-CHT was 5.5 years. Fifty four pts (67%) had radical resection after neoadjuvant RT/RT-CHT and 27 (33%) were still unresectable. CEA serum concentration decrease or level below 5ng/ml (group A) was observed in 63 pts (77%), CEA serum concentration increase/level above 5ng/ml (group B) in 18 (22%). In univariate analysis pts in group A had better overall survival compared to group B (p=0.039, median OS of 40 months vs 87 months, respectively). Five-year OS was 62% in group A compared to 30% in group B. Moreover, pts who received RT-CHT had better 5-year OS compared to RT (63 vs 44%) respectively (p=0.04). Pts after radical resection had better 5-year OS than those still uresectable (71% vs 21%, p=0,000). Significant factors were then checked in multivariate analysis. Only radical surgery had reached statistical significance (p=0,000) for OS. Conclusion Pts with post-treatment serum CEA concentration decrease or level below 5 ng/ml tend to have better overall survival compared to those in whom CEA concentration did not decrease after the neoadjuvant treatment. Post-treatment decrease in serum CEA concentration in primary unresectable rectal cancer patients who received definitive RT/RT-CHT can be a useful predictor of outcome. Analysis on larger group of pts is needed to evaluate these results. PO-1096 Prediction of pathologic response by clinical characteristics following preoperative CRT in LARC J. Kim 1 , B. Kang 2 , C. Song 1 , S. Kang 3 1 Seoul National University Bundang Hospital, Radiation Oncology, Seongnam, Korea Republic of ; 2 Seoul National University Bundnag Hospital, Radiation Oncology, Seongnam, Korea Republic of ; 3 Seoul National University Bundang Hospital, Surgery, Seongnam, Korea Republic of Purpose or Objective This study aims to identify pretreatment clinical predictors of good pathologic tumor response after preoperative chemoradiotherapy (CRT) in locally advanced rectal

modulated radiotherapy (SIB-IMRT) (220 cGy/die, total dose 5500 cGy). We administered: 5-fluoracil and leucovorin or capecitabine, alone or in association with cisplatin (Plafur) or oxaliplatin (Capeox). In patients enrolled in an Italian trial, oxaliplatin was associated to raltitrexed (Tomox). Four groups of patients were identified: fluoropirimidine chemotherapy plus 50 Gy (Fluoropirimidine group), Plafur chemotherapy plus 50 Gy (Plafur group), Tomox-Capox chemotherapy plus 50 Gy (Tomox-Capox group) and capecitabine with a dose escalation up to 55 Gy (Dose intensification group). pCR was evaluated according to Mandard tumor regression grade (TRG). The Kaplan-Meier method was used to estimate OS, DFS and LC. Results Of the 322 patients analyzed, 80.8% had cT3 tumors and 303 (94.1%) underwent surgery. Table 1 reported the percentage of patients in each sub-group and the number of patients performing sphincter-saving surgery. The primary endpoint was tumor regression grade rate: TRG1 was obtained in 81 (26.7%) patients, TGR2 in 46 (15.1%), TRG3 in 100 (33.0%), TRG4 in 69 (22.8%) and TRG5 in 5 (1.7%) patients. Data were missing for 2 patients (0.7%). The major pathological response (TRG1-2) rate was 41.8%. The proportion of patients with a TRG 1-2 was higher in the Dose intensification group compared to the Fluoropirimidine, Plafur and Tomox-Capeox group, with a statistical significance difference in the dose intensification group (p= 0.046) (Table 1). The 5- and 10- year OS, DFS and LC rates were 82.5%±2.5% and 65.5%±3.8%, 81.2%±2.4% and 79.3%±2.9%, 93.1%±1.7% and 90.5%±2.1%, respectively. The different rates of 5- and 10- year OS, DFS and LC for patients with TRG1-2 and TRG3-5 and the outcomes for the different sub-groups were reported in Table 2.

Conclusion Neoadjuvant CRT in LARC patients resulted in favorable long-term oncologic outcomes with high pCR rate (TRG1- 2: 41.8%). Dose intensification strategy seems to obtain a major pathological response higher respect to drugs combination. PO-1095 Does CEA decrease after radical treatment of unresectable rectal cancer predicts the outcome? M. Kraszkiewicz 1 , A. Napieralska 1 , L. Miszczyk 1 , W. Majewski 1 1 Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Radiotherapy Department, Gliwice, Poland

Purpose or Objective