ESTRO 37 Abstract book

S58

ESTRO 37

SP-0113 Circulating tumour DNA as a therapeutic biomarker for radiotherapy S. Bratman 1 1 Princess Margaret Cancer Centre, Department of Radiation Oncology, Toronto, Canada Abstract text 'Precision radiation medicine' requires robust biomarkers to help refine the delivery of radiotherapy. Radiation oncologists currently have few molecular tools at their disposal for predicting or rapidly assessing treatment efficacy. Circulating tumour DNA (ctDNA) is an attractive source of cancer biomarkers because it contains many of the same genetic and epigenetic aberrations that are present in tumours and can be non-invasively and repeatedly accessed from peripheral blood. While most of the clinical impact of ctDNA analysis has thus far been observed among patients with metastatic incurable cancer, emerging ctDNA detection technologies are now providing an opportunity to influence patients with localized potentially curable cancer. Possible uses of ctDNA analysis for such patients include prognostication and risk stratification, prediction of treatment response, longitudinal monitoring for adaptive treatment, and evaluating minimal residual disease. In this talk, I will describe recent advances in ctDNA technologies and potential clinical applications of ctDNA analysis throughout the therapeutic course. Furthermore, I will illustrate how ctDNA analysis could someday guide radiotherapy delivery by revealing differences in tumour radiophenotype. Because ctDNA is released into the bloodstream during the process of tumour cell death, a transient elevation in ctDNA levels could reflect rapid response and treatment sensitivity. Thus, by displaying dynamic changes with treatment, ctDNA as a biomarker for radiation response could enable new personalized treatment approaches. The path toward implementation of such strategies into the routine clinical practice of radiation oncology will be discussed. SP-0114 Circulating tumour cell (CTC) analysis in radiotherapy patients A. Hudson 1 1 University of Manchester, Division of Molecular and Clinical Cancer Sciences, Manchester, United Kingdom Abstract text Circulating tumour cells (CTCs) are neoplastic cells derived from solid malignancies that can be extracted from the bloodstream. Using advanced technologies applied to a simple blood test, CTCs are isolated from the blood to provide essential information about the solid tumour from which they originate. These liquid biopsies allow genetic, proteomic, and biological assessment of tumours without the need for an invasive biopsy. Furthermore the ease and safety of CTC collection allows temporal assessment of tumour biology with minimal distress to the patient. Radiotherapy patients in particular may benefit from CTC analysis as poor performance status, co-morbidities, or location of the tumour often precludes any type of invasive biopsy in this patient population. Clinical research in different cancer subtypes has demonstrated prognostic and predictive utility for CTC counts indicating a potential for them to be used as biomarkers for treatment decisions in the future. Smaller studies have been done to assess CTC number both during and after radiotherapy with variable findings that are likely confounded by the different extraction methods used. In a research setting, capturing complete tumour cells for analysis affords potential rewards for investigating radiobiology such as the ability to assess markers of cell cycle distribution and DNA damage, receptor expression, and the co-occurrence of mutations in treatment resistance. The recently

Conclusion The minimum dose to the left atrium finding suggests that limiting the low dose-bath to the cardiovascular system is important to prolong survival after chemo- radiation for NSCLC. In addition to performance status assessments, cardiovascular functional test acquired prior to treatment could further guide in treatment protocol stratification.

Symposium: Blood borne biomarkers