ESTRO 38 Abstract book

S604 ESTRO 38

association with biochemical recurrence (BCR) was assessed using Cox regression models and Kaplan-Meier survival curves with log-rank tests. Results After adjustment for the established risk factors including age, PSA at diagnostic, Gleason score and androgen- deprivation therapy use; 17 htSNPs in ACVRL1, ERCC1 and 3, MGMT, MSH6, RAD51A, TP53BP1 and XRCC6, were initially found to be associated with an altered risk of BCR, with adjusted hazard ratios (HR adj. ) ranged between 0.27 - 12.39 ( P ≤ 0.05). Upon adjustment for multiple testing, one marker remained significant (q<0.001). Compared to carriers of the ERCC3 rs4150499 T allele, patients homozygous for C allele (n= 23) had a significant higher risk of BCR with a HR of 12.39 (IC 95% 4.22-36.39; p<0.0001; q<0.001). The Kaplan-Meier survival curve revealed a median BCR-free survival time reduced from 213 ± 7 to 99 ± 12 months (log-rank P <0.00001) for homozygous carriers of the ERCC3 rs4150499 C allele compare to non-carriers. Conclusion This study suggests an association of the rare intronic variant (Frequency=0.05 in the study) of the ERCC3 with an elevated risk of BCR after PIPB. An independent validation is required whereas the underlying biological mechanism remained to be assessed. PO-1089 Improvement and optimization of γH2AX foci assay as a predictive tool for radiation sensitivity T. Rassamegevanon 1 , S. Löck 1,2 , M. Baumann 1,2,3,4,5 , M. Krause 1,2,3,4,5 , C. Von Neubeck 1,4 1 OncoRay – National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus- Technische Universität Dresden- Helmholtz-Zentrum Dresden - Rossendorf, Dresden, Germany ; 2 Department of Radiotherapy and Radiation Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus- Technische Universität Dresden, Dresden, Germany ; 3 Helmholtz-Zentrum Dresden - Rossendorf, Institute of Radiooncology – OncoRay, Dresden, Germany ; 4 German Cancer Consortium DKTK- Partner Site Dresden, and German Cancer Research Center DKFZ, Heidelberg, Germany ; 5 National Center for Tumor Diseases NCT- Partner Site Dresden- Germany: German Cancer Research Center DKFZ- Heidelberg- Germany- Faculty of Medicine and University Hospital Carl Gustav Carus- Technische Universität Dresden- Dresden- Germany, and- Helmho, Purpose or Objective Prediction of tumor radiation response using molecular biomarkers has been considered as a promising approach for treatment individualization to improve therapeutic outcome. Phosphorylation of histone H2AX (γH2AX) is one of the earliest response to DNA double strand break induction. Detection of γH2AX focus formation on ex vivo irradiated solid tumor biopsies demonstrated a high potential as a predictive assay for intrinsic radiosensitivity [1]. We aims to further optimize and develop the ex vivo γH2AX foci assay to increase clinical relevance. Material and Methods Tumor xenograft models of human head and neck squamous cell carcinoma were used in this study. Tumor-bearing mice ( in vivo ) and xenograft-derived biopsies ( ex vivo ) were irradiated with 0 - 8Gy; fixed and paraffin embedded 24 h post irradiation. The γH2AX foci were visualized by immunostaining. Manual quantification of γH2AX foci was performed solely in perfused regions determined by pimonidazole (hypoxic marker) and BrdU (proliferation marker) staining. Results This study is focused on two aspects: a) Tumor heterogeneity: To study the effect of tumor heterogeneity in the ex vivo γH2AX foci assay, we analyzed multiple equally treated xenograft tumor specimens (sham- and 4 Gy irradiated). The outcome

GFP), whose miR-221 expression levels equal the non- transduced cells. The cells were irradiated at doses of 0 to 8 Gy using a Cs 137 gamma irradiation source. Clonogenic cell survival with respect to radiation and miR-221 overexpression was examined using colony formation assays. Effects of miR-221 expression combined with irradiation on proliferation (cell counting) and migration (wound scratch assays) were analyzed. qRT-PCR was performed to determine miR-221 expression changes upon irradiation. Results miR-221 overexpressing cells showed significantly higher migration capacity in both cell lines. Remarkably, the migration capacity remained constant even upon 8 Gy ionizing radiation treatment. In parallel, miR-221 overexpressing cells showed elevated proliferation in both cell lines 72 hours after radiation. The reduction of cell numbers upon radiation was more pronounced in MDA-MB- 231 than in SKBR3. The clonogenic survival assays confirmed that miR-221 overexpressing SKBR3 cells were more radioresistant than the control. In MDA-MB-231, no significant effect of miR-221 knock-down on clonogenic survival was observed. Additionally, irradiation did not alter the miR-221 expression levels significantly. Conclusion The results of our experiments show reproducibly increased migration and proliferation of mammary carcinoma cell lines SKBR3 and MDA-MB-231 upon miR-221 overexpression. The effect of miR-221 on migration remains constant upon irradiation whereas proliferation decreases after radiation treatment. Additionally, the proliferation assays show a drastic reduction of viable cells upon irradiation, whereas no strong reduction of migration upon radiation can be observed. This leads to the assumption that irradiation might increase migration levels. Regarding the consequences for a personalized radiotherapy in the future, miR-221 overexpression in TNBC patients indicates a higher risk of metastasis development. PO-1088 DNA repair genes polymorphisms as biomarkers of tumor control in LDR BT prostate cancer patients D. Carignan 1 , É. Vigneault 2 , L. VIlleneuve 3 , S. Desjardins 4 , S. Magnan 2 , P. Després 5 , A. Martin 2 , W. Foster 2 , C. Guillemette 6 , É. Lévesque 7 1 CHU de Québec-UL Research Center, Oncology, Quebec, Canada ; 2 CHU de Québec-UL, Radio-Oncology, Quebec, Canada ; 3 CHU de Québec-UL Research Center and Faculty of Pharmacy- Laval University, Pharmacognenomics Laboratory, Quebec, Canada ; 4 CHU de Québec-UL Research Center, Endocrinology and Nephrology, Quebec, Canada ; 5 CHU de Québec-UL Research Center, Physics- Physical Engineering and Optics Department- Laval University, Quebec, Canada ; 6 CHU de Québec-UL Research Center and Faculty of Pharmacy- Laval University, Pharmacognenomics Laboratory and Canada Research Chair in Pharmacogenomics, Quebec, Canada ; 7 CHU de Québec- UL Research Center, Endocrinology and Nephrology and CHU de Québec-UL Hemato-Oncology department, Quebec, Canada Purpose or Objective To evaluate the association of inherited germline variations in DNA repair associated genes with tumor control in patients treated with permanent implant prostate brachytherapy (PIPB). Material and Methods The cohort consists of 478 I-125 PIPB patients with a median follow-up of 51 months after seeds implantation. Upon consent of patients, DNA was prepared from mononuclear cells and genotyped for 215 haplotype tagging single nucleotide variations (htSNPs) in genes of DNA damage response and repair pathways. Their