ESTRO 2020 Abstract book

S66 ESTRO 2020

using the QIAamp-DNA-Stool-Mini-Kit, bacterial 16S ribosomal-RNA reads analyzed with QIIME software and pooled in Operational Taxonomic Units (OTU) with Uclust software. Pre-RT and post-RT OTUs at genus and species taxonomic levels were considered. Modulation was evaluated by Wilcoxontest, both on the whole population and after stratification with respect to acute GU and GI tox (CTCAE): Grade 0 (G0) vs Grade 1 (G1) vs Grade 2 (G2) Results 135 pts were included, 157 genera and 412 bacterial species were identified. 59/157 genera and 132/412 species were found in at least 10% of pts and included in the analyses. 7 genera (Bilophila, Faecalibacterium, Flavonifractor, Gemmiger, Phascolarctobacterium, Roseburia, Sutterella) and 4 species (Blautia producta, Faecalibacterium prausnitzii, Roseburia faecis, Ruminococcos bromii) were significantly modulated by RT (p<0.01 and <0.001, for genera and species, respectively), details in fig 1. Of interest, Ruminococcus bromii is a keystone species for the degradation of resistant starch in the colon and a possible relationship between Roseburia faecis and irritable bowel syndrome was recently proposed. When considering GI tox, 29 (22%), 30 (22%) and 76 (56%) pts reported G0, G1 and G2 events, respectively. No significant MB modulation was found in G0 (at p level<0.01), while 7 genera were significantly modulated by RT in G1: Faecalibacterium, Flavonifractor, Gemmiger, Odoribacter, Phascolarctobacterium, Roseburia, Sutterella (p range: 0.003-0.008). 3 genera were significantly modulated in G2: Akkermansia, Bilophila, Faecalibacterium (p range: 0.001-0.008). When considering GU tox, 80 (59%) and 42 (31%) pts reported G1 and G2 events, respectively. No significant MB modulation (at p level<0.01) in G0 was identified.5 genera were modulated in G1: Faecalibacterium, Flavonifractor, Phascolarctobacterium, Ruminococcus, Sutterella (p<0.01). Lactobacillus was significantly modulated exclusively in pts with G2 GU tox (p=0.008). The detailed results about association between tox and MB species are reported in fig 2

Conclusion This analysis demonstrated the possibility to quantitatively study RT-induced alteration of gut MB in a clinical setting including “real world” pts. Moreover, association between acute tox and different pattern of MB alteration was highlighted: a dysbiotic MB becomes a strongly suspected actor in appearance and evolution of RT-induced tox PH-0120 The influence of telomere length on mortality in prostate cancer patients treated with radiotherapy. T. Langsenlehner 1 , K. Lukasiak 2 , E. Thurner 2 , U. Langsenlehner 3 , H. Stranzl-Lawatsch 2 , W. Renner 4 1 Medical University of Graz, Department of Radiation Oncology, Graz, Austria ; 2 Medical University of Graz, Department of Therapeutic Radiology and Oncology, Graz, Austria ; 3 FÄZ Graz, Department of Internal Medicine, Graz, Austria ; 4 Medical University of Graz, Clinical Institute of Medical and Chemical Laboratory Diagnostics, Graz, Austria Purpose or Objective Telomeres, the end parts of linear chromosomes, play a crucial role in protecting DNA during each cell division. Telomere shortening has been associated with a higher risk of cancer and its progression, in contrast, previous studies also reported an association between shorter telomere length and improved outcome for a variety of cancers. The purpose of this study was to evaluate the relationship between leucocyte relative telomere length (RTL) and mortality in prostate cancer patients. Material and Methods Blood samples from 533 patients were gathered before start of irradiation for prostate cancer. RTL of peripheral blood leucocytes was determined by a quantitative polymerase chain reaction method and was divided into quartiles based on the distribution in the entire cohort. The study endpoints were overall and cancer- specific mortality. Results During a median follow-up time of 149 months, 188 patients (35.3%) died, 58 patients (10.9%) died of prostate cancer. Univariate Cox regression analysis revealed a significant association of RTL quartiles and overall mortality (HR 1.20; 95% Cl 1.05 – 1.36; p = 0.006). In multivariate Cox regression, which included age at