PS02.195: CIRCULATING TUMOUR DNA HAS UTILITY IN THE CLINICAL MANAGEMENT OF ESOPHAGEAL CANCER

Abstract

Abstract Background Cell-free DNA, a consequence of normal cell death and apoptosis, is found in the blood of all individuals. In cancer patients, a proportion of circulating cell free DNA will be derived from tumour cells, and is termed circulating tumour DNA (ctDNA).We have developed a blood-based ‘liquid biopsy’ to detect ctDNA in plasma of esophageal cancer patients. Methods Tumour, buffy-coat (germline) and plasma samples were obtained from 28 esophageal cancer patients at the time of diagnosis. Serial blood samples were collected from 8 patients. Somatic DNA mutations in 9 genes (TP53, ARID1A, SMAD4, CDKN2A, SMARCA4, NRG1, APC, PIK3CA and KRAS) were evaluated in tumour biopsies and plasma using targeted sequencing. Tumour specific mutations were confirmed by droplet digital PCR, which was used to track patient-specific ctDNA in plasma from serially collected blood samples. Results Somatic mutations in at least one of the targeted genes were detected in 19/28 (68%) tumour biopsies. The same mutations were detected in ctDNA from plasma in 9/19 (48%) patients. Additional mutations that were not detected in the tumour biopsies were detected in plasma DNA from 2 patients, highlighting the issues of intra-tumoural heterogeneity and sampling bias of tumour biopsies. ctDNA was more frequently detected in patients with advanced disease where it represented a greater proportion of the total cell-free plasma DNA than in patients with localised disease. In patients with serial samples, levels of ctDNA correlated with response to treatment, and rises in ctDNA could be detected prior to clinical evidence of relapse. Conclusion Detection of ctDNA using targeted sequencing and digital PCR is feasible in the majority of esophageal cancer patients, particularly those with advanced disease. Dynamic changes in ctDNA levels reflect response to treatment and disease relapse as determined by conventional clinical imaging. We conclude that ctDNA levels can provide supplemental evidence regarding disease staging, as well as prognostic and predictive information that can inform therapeutic pathway decisions in esophageal cancer patients. Disclosure All authors have declared no conflicts of interest.