PS02.083: CIRCULATING CELL FREE TUMOR DNA FOR DISEASE MONITORING AFTER NEOADJUVANT CHEMORADIOTHERAPY FOR ESOPHAGEAL CANCER: PROOF-OF-PRINCIPLE

Abstract

Abstract Background An active surveillance approach has been proposed for patients with a clinically complete response (cCR) after neoadjuvant chemoradiotherapy (nCRT) in esophageal cancer (SANO trial). To justify renouncing surgical resection, patients with residual disease after nCRT should be accurately identified. However, substantial residual disease (TRG3–4) cannot be detected in 10% of patients with current diagnostic tests (preSANO trial). Circulating cell free tumor DNA (ctDNA) potentially improves detection of residual malignancy after nCRT and could be used for disease monitoring. The objective of this study was to investigate the feasibility of using ctDNA as biomarker for disease status after nCRT in esophageal cancer. Methods Twelve typical patients from the preSANO trial with variable pathological responses to nCRT were included. Blood was drawn and processed pretreatment. The feasibility of detecting TP53 mutations in baseline tumor biopsies was investigated using a next generation sequencing (NGS) panel. Subsequently, baseline blood samples of patients in whom specific TP53 mutations could be identified in baseline tumor biopsies or the surgical resection specimen were analyzed for ctDNA using cell free DNA NGS kits with single molecule barcoding (Oncomine Thermo Fisher). Results Baseline biopsy samples were available in 8 out of 12 patients. In 7 of these 8 patients (88%) specific TP53 mutations could be identified in their baseline biopsies. In 11 out of 12 patients (92%) specific TP53 mutations could be identified in baseline biopsies or the resection specimen. Eight of these 11 mutations were potentially detectable by the Oncomine panel. The panel detected TP53 mutational ctDNA in 4 of these 8 samples (50%). Conclusion Specific and clonal TP53 mutations can be identified in pretreatment biopsy samples and in surgical resection specimens of patients with esophageal cancer. These mutations can be matched to ctDNA identified in blood samples. Hence, ctDNA analyses in blood samples can potentially be used for disease monitoring during active surveillance and for disease monitoring in follow-up after surgical resection. Disclosure All authors have declared no conflicts of interest.