ESTRO 2020 Abstract Book

S550 ESTRO 2020

a median follow-up of 30 (range, 3-131) months, the median OS was 58.8 months and 3-year, 5-year rates were 58% and 47%, respectively. The median RFS was 24 months and 3-, and 5-year rates were 47% and 39%, respectively. According to the stages (I, II, and III), median OS rates were 59, 24, and 15 months, and median RFS rates were 59, 15, and 12 months. In the univariate analysis for OS, older age (≥67) and SCLC-mixed histology are statistically associated with poor prognosis (p=0.019, p=0.001 (vs. pure LCNEC), and 0.015 (vs. NSCLC-mixed)), respectively. These 2 factors were independently associated with OS also in multivariate analysis (p=0.036 (HR 2.805 (95% CI: 1.068 – 7.365)), 0.003 (HR 16.125 (95% CI: 2.615-99.434)), and 0.015 (HR 11.905 (95% CI: 1.618– 90.909)). Recurrences occur in 17 patients (44%). Most of the recurrence patterns were very extensive even at the first recurrence; 14 distant metastases (82%), 8 local recurrences, and 8 regional (mediastinal lymph node) recurrences. Regional recurrences occurred in 57% of pN1 stage tumors, regardless of other risk factors, which was much higher than that of pN0 stage tumors (p=0.047). Conclusion Pulmonary LCNEC cohort demonstrated that our treatment policy might achieve reasonable OS and RFS. Older age and mixed histology with SCLC made the overall prognosis even worse, regardless of the stage, which proposed the need for more active adjuvant treatment strategies by a multidisciplinary approach for surgically treated LCNEC. PO-1033 The result of type C thymic epithelial tumor: multimodality treatment combined with radiotherapy G. Yang 1 , H.K. Byun 1 , J. Kim 1 , J. Lee 1 , W.H. Lee 1 , B.M. Lee 1 , A.J. Yang 1 , J.Y. Moon 1 , J. Cho 1 1 Yonsei Cancer Center, Radiation Oncology, Seoul, Korea Republic of Purpose or Objective Owing to the rarity of the disease and paucity of clinical data, the treatment strategy of thymic epithelial tumor (TET) varies among institutions and the role of radiotherapy (RT) in the treatment of type C TET is not yet definitely determined. The aim of this study was to report the clinical outcomes of patients with type C TET including survival rates, patterns of failure and toxicity of multimodality treatment. Material and Methods Ninety-two patients diagnosed with type C TET who were treated between November 2006 and December 2018 were included. Among these patients, patients who were not treated with RT or who received RT to lesions other than thymus were excluded (n=20). Thus, a total of seventy-two patients with type C TET treated with RT combined with surgery and/or chemotherapy were analyzed. As for target volume, regional nodal areas were electively covered only when involved at initial diagnosis. 3D-CRT and IMRT were used in 30 (41.7%) and 41 (56.9%) patients, respectively. Dose and fractionation varied according to treatment aims. The clinical outcomes, including patterns of failure, survival and toxicity were analyzed. Results With a median follow-up period of 25.9 months (range, 3.7-137.3 months), the 5-year rates of overall survival, progression-free survival, local recurrence-free survival rates were 73.3%, 52.9%, 94.9%, respectively, which were better than those of historical reports. During the follow- up period, 15 deaths and 25 recurrences were observed. Regarding RT field, no isolated infield or marginal failure were observed. Outfield failure was the most common pattern of failure (n=20, 80%) followed by marginal + outfield (n=3, 12%), and infield + outfield failure (n=2, 8%). No failure at the primary tumor site was observed. The failure patterns were also analyzed according to International Thymic Malignancy Interest Group (ITMIG) guidelines, which classified failure sites into local, regional and distant failure. Distant failure was most

common (n=16, 64%), followed by regional failure (n=6, 24%). As for the seven patients who were irradiated including the involved supraclavicular area, no failure within the supraclavicular area occurred. In terms of toxicity, no patient developed grade 3 or higher RT-related toxicity. Patients treated with IMRT developed less overall toxicity compared to patients treated with 3D- CRT (31.7% vs. 76.7%, p=.001). Conclusion The 5-year overall survival and progression-free survival rates in our study were favorable compared to previous studies. In addition, an excellent 5-year local recurrence- free survival rate was achieved by RT. Our experiences suggest that RT should be incorporated into the multidisciplinary management of type C TET to enhance oncologic outcomes, even in stage IVB patients with regional node metastases. In addition, RT with advanced precision technique such as SIB-IMRT reduced treatment related toxicity while maintaining good local control. PO-1034 Chemoradiation-induced intratumoral immune microenvironment changes in oesophageal cancer C. Yip 1 , J.P.S. Yeong 2 , W.Q. Leow 3 , L.M. Wang 4 , L.A.L. Lee 5 , T.K.H. Lim 3 , T.R. Siow 1 , F.W.T. Lim 1 , M.L.C. Wang 1 , S.Z. Ho 1 , F. Wang 1 , M.C. .H. Ng 6 , S.J. Ong 6 , J.Y.C. Lam 6 , W.K. Wong 7 , H.S. Ong 7 , E. Lim 7 , A.K.H. Eng 7 , C.H. Lim 7 , W.H. Chan 7 , A. .S.Y. Wong 8 , J. Lee 8 , J. Lin 8 , E. Ong 1 , M.L.K. Chua 1 1 National Cancer Centre Singapore, Department of Radiation Oncology, Singapore, Singapore ; 2 A*STAR, Institute of Molecular and Cell Biology, Singapore, Singapore ; 3 Singapore General Hospital, Anatomical Pathology, Singapore, Singapore ; 4 Changi General Hospital, Pathology, Singapore, Singapore ; 5 Sengkang General Hospital, Pathology, Singapore, Singapore ; 6 National Cancer Centre Singapore, Medical Oncology, Singapore, Singapore ; 7 Singapore General Hospital, Upper Gastrointestinal ＆ Bariatric Surgery, Singapore, Singapore ; 8 Changi General Hospital, General Surgery, Singapore, Singapore Purpose or Objective We aimed to evaluate the intratumoral immune microenvironment changes after chemoradiation (CRT) in Patients with histologically proven oesophageal cancer who were planned for neoadjuvant CRT were prospectively recruited. All patients were treated with VMAT (41.4Gy in 23 fractions) and concurrent weekly Carboplatin (50mg/m 2 )/Paclitaxel (AUC 2) followed by surgery. Diagnostic biopsy and resected primary tumour FFPE specimens were retrieved for multiplex immunofluorescence (mIF) analysis which allows labelling of up to 7 stains on a single tissue section. Each section was stained for PD-L1, FOXP3, CD68, CD3, CD8 and cytokeratin (CK). Images were acquired using a Vectra 3 pathology imaging system microscope and analysed using inForm version 2.4.1 software. The average cell count was calculated to estimate the expression of each immune marker. Pathological tumour response (TRG) was centrally reviewed using the Mandard grading system. Disease relapse and survival outcomes were obtained. Results For this preliminary analysis, 4 patients had paired tumour samples available for evaluation (3 SCC; 1 adenocarcinoma). All patients received full dose RT. Three patients completed all 5 cycles of chemotherapy and 1 patient had 4 cycles. Median follow-up was 15.8 months, oesophageal cancer. Material and Methods Poster: Clinical track: Upper GI (oesophagus, stomach, pancreas, liver)