Abstract book - ESTRO meets Asia

S94 ESTRO meets Asia 2018

1 Fudan University Shanghai Cancer Center, Radiation Oncology, Shanghai, China

response (TRG 2), one had minimal response (TRG 4) and four had no response (TRG 5). Even patients who had MRI TRG 5 showed pathological complete response. MSI IHC was done in 17 and all were MSI stable. Patients who underwent surgery had mean follow up of 16 months. On correlation of MRI TRG with pathological TRG, two out of two MRI TRG 5 patients and three out of ten MRI TRG 4 patients had complete pathological response (TRG 1).Three out of ten MRI TRG 4 patients had near complete pathological response (TRG 2).Of the 6 patients who had complete pathological response(TRG 1), two were MRI TRG 5, three were MRI TRG 4 and one was MRI TRG 3. Conclusion The predictive value of MRI down staging in Signet Ring Cell Carcinoma Rectum following neoadjuvant LCCRT is not often in concurrence with histopathological response and needs to be interpreted with caution. The pathological complete response rate seen in this cohort appears to be encouraging and needs to be estimated in a larger series. Hence long course chemo irradiation may play a significant role in the management of these tumours. MSI status with IHC technique is useful but may be sub optimal and it should preferably be assessed using PCR techniques in future studies. PO-228 Aneuploidy of chromosome 8 and mutation of CTCs predict pathCR in the treatment of rectal cancer J. wan 1 , Z. zhang 1 1 Fudan University Shanghai Cancer Center, radiation oncology, Shanghai, China Purpose or Objective Identifying patients who may or may not achieve pathologic complete response (pathCR) would allow for treatment with alternative approaches in the preoperative setting. The aim of the current study was to investigated whether aneuploidy of chromosome 8 and mutations of circulating tumor cells could predict the response of patients with rectal cancer to preoperative chemoradiotherapy. Material and Methods We recruited 33 patients with locally advanced rectal cancer (cT3-T4 and/or cN+) treated with neoadjuvant chemoradiotherapy at between September 2014 and March 2015. Blood samples were collected from 33 patients with pre-chemoradiotherapy rectal cancer. Results We found that ≥5 copies of chromosome 8 was associated with pathCR (univariate logistic regression, P=0.042). Of the 6 patients whose circulating tumor cells had <5 copies of chromosome 8, 3 achieved pathCR (3/6, 50%), and of the 27 patients whose circulating tumor cells had ≥5 copies of chromosome 8 obtained 3 pathCR (3/27, 11.1%; Chi-square test, P=0.0255). Of the 33 patients with mutations assessed, 8 significant nonsynonymous mutations in CTCs were identified as associated with pathCR (Chi-square test, P-values range, 0.0004-0.0298; mutations in ARID1A, HDAC1, APC, ERBB3, TP53, AMER1 and AR). Conclusion Our results suggest that ≥5 copies of chromosome 8 and 8 nonsynonymous mutations in ARID1A, HDAC1, APC, ERBB3, TP53, AMER1 AR in CTCs were associated with pathCR. This conclusion should be validated further in larger prospective studies and the long-term follow-up survival data of our study will also be reported in the future. PO-229 Poor-prognosis Locally Advanced Rectal Cancer is Defined by a Molecularly Distinct Subtype J. Zhang 1 , L. Shen 1 , Y. Wang 1 , X. Sun 1 , Y. Deng 1 , H. Zhang 1 , R. Hu 1 , W. Yang 1 , J. Yang 1 , Z. Zhang 1 , W. Zou 1 , L. Yang 1 , J. Wan 1 , F. Xia 1 , J. Zhu 1 , Z. Zhang 1

Purpose or Objective TNM stage is still the only prognostic tool used in clinical practice to treat patients but it fails to accurately predict outcomes. Categorization of locally advanced rectal cancers into distinct subtypes using a combination of qPCR-based biomarkers could provide insight into We used a qPCR-based assay to detect 30 genes (LARCassigner-30) in 197 locally advanced rectal cancer samples, collected prospectively from patients treated with neoadjuvant chemoradiation and surgery from January 2007 to December 2012 in Fudan University Shanghai Cancer Center. 197 patients were randomly divided into training queuing of 98 cases and validation of the cohort of 99 cases. Median follow-up time is 58 months. Association with 5-year overall survival, disease- free survival, recurrent rate and metastatic rate was evaluated using Cox proportional hazards models. Results Baseline clinical characteristics and postoperative pathological features were similar between the training cohort and the validation cohort. The overall survival rate of LARCassigner-30 type 1 patients was lower than that of type 2 patients in the training and validation cohorts (p< 0.01), tumor-free survival rate decreased (p <0.01); local recurrence rate increased (p <0.01), distant metastasis rate increased (p <0.01), the difference was statistically significant. In the training cohort, LARCassigner-30 type 1 patients with locally advanced rectal cancer were found to have poorer response to neoadjuvant chemoradiation than type 2 patients (p=0.023), but they were not verified in the validation cohort. Conclusion We developed qPCR-based classifiers LARCassigner-30 that performs well at predicting the outcomes in locally advanced rectal cancer. PO-230 Dosimetric comparison of short course radiotherapy techniques in locally advanced rectal cancer F. Ho 1 , Y.Y. Soon 1 , C.W. Tan 1 , D. Chen 1 , B. Vellayappan 1 , J. Tey 1 1 National University Cancer Institute, Radiation Oncology, Singapore, Singapore Purpose or Objective Neoadjuvant short course radiotherapy is one of the standard approach for resectable locally advanced rectal adenocarcinoma. Traditionally, three-dimensional radiotherapy(3DCRT), is used to radiate the primary and the draining nodal basin. With the advent of newer conformal radiotherapy techniques like intensity modulated radiotherapy (IMRT) and volumetric modulated arc radiotherapy(VMAT), there is a potential to improve target coverage and reduce toxicity to organs at risk (OAR). Material and Methods CT simulation datasets of 10 patients with locally advanced rectal cancer were utilized for this study. All patients were simulated in the prone position. The clinical target Volume (CTV) included the gross tumour volume and the draining pelvic lymph node chains. This was expanded by an additional 5mm margin to generate the planning target Volume (PTV). All patients had a prescription dose of 25Gy in 5 fractions to the PTV. IMRT and VMAT plans were planned on the Monaco planning system and plans were optimised to meet standard dose constraints for the bladder, small bowel, femoral heads and bone marrow. 3DCRT plans were planned on the XiO treatment planning system. Three plans were generated for dosimetric comparison (3DCRT, IMRT, VMAT). We variability in outcomes. Material and Methods