Detection of Circulating Tumor DNA in Plasma: A Potential Biomarker for Esophageal Adenocarcinoma.

Background: Recent literature has demonstrated the potential of "liquid biopsy" and detection of circulating tumor (ct)DNA as a cancer biomarker. However, to date there is a lack of data specific to esophageal adenocarcinoma (EAC). This study was conducted to determine how detection and quantification of ctDNA changes with disease burden in patients with EAC and evaluate its potential as a biomarker in this population.

Methods: Blood samples were obtained from patients with stage I to IV EAC. Longitudinal blood samples were collected from a subset of patients. Imaging studies and pathology reports were reviewed to determine disease course. Tumor samples were sequenced to identify mutations. Mutations in plasma DNA were detected using custom, barcoded, patient-specific sequencing libraries. Mutations in plasma were quantified, and associations with disease stage and response to therapy were explored.

Results: Plasma samples from a final cohort of 38 patients were evaluated. Baseline plasma samples were ctDNA positive for 18 patients (47%) overall, with tumor allele frequencies ranging from 0.05% to 5.30%. Detection frequency of ctDNA and quantity of ctDNA increased with stage. Data from longitudinal samples indicate that ctDNA levels correlate with and precede evidence of response to therapy or recurrence.

Conclusions: ctDNA can be detected in plasma of EAC patients and correlates with disease burden. Detection of ctDNA in early-stage EAC is challenging and may limit diagnostic applications. However, our data demonstrate the potential of ctDNA as a dynamic biomarker to monitor treatment response and disease recurrence in patients with EAC.