Limited Sensitivity of Circulating Tumor DNA Detection by Droplet Digital PCR in Non-Metastatic Operable Gastric Cancer Patients.

Luc Cabel,Charlotte Proudhon,Sophie Vacher,Francois-Clement Bidard,Virginie Bernard,Sylvain Baulande,Christophe Louvet,Mostefa Bennamoun,Pascale Mariani,Ivan Bieche,David Fuks,Marine Lefevre,Charles Decraene,Jean-Yves Pierga,Jean-Marc Ferraz

doi:10.3390/cancers11030396

Abstract

This study was designed to monitor circulating tumor DNA (ctDNA) levels during perioperative chemotherapy in patients with non-metastatic gastric adenocarcinoma. Plasma samples were prospectively collected in patients undergoing perioperative chemotherapy for non-metastatic gastric adenocarcinoma (excluding T1N0) prior to the initiation of perioperative chemotherapy, before and after surgery (NCT02220556). In each patient, mutations retrieved by targeted next-generation sequencing (NGS) on tumor samples were then tracked in circulating cell-free DNA from 4 mL of plasma by droplet digital PCR. Thirty-two patients with a diagnosis of non-metastatic gastric adenocarcinoma were included. A trackable mutation was identified in the tumor in 20 patients, seven of whom experienced relapse during follow-up. ctDNA was detectable in four patients (N = 4/19, sensitivity: 21%; 95% confidence interval CI = 8.5–43%, no baseline plasma sample was available for one patient), with a median allelic frequency (MAF) of 1.6% (range: 0.8–2.3%). No patient with available plasma samples (N = 0/18) had detectable ctDNA levels before surgery. After surgery, one of the 13 patients with available plasma samples had a detectable ctDNA level with a low allelic frequency (0.7%); this patient experienced a very short-term distant relapse only 3 months after surgery. No ctDNA was detected after surgery in the other four patients with available plasma samples who experienced a later relapse (median = 14.4, range: 9.3–26 months). ctDNA monitoring during preoperative chemotherapy and after surgery does not appear to be a useful tool in clinical practice for non-metastatic gastric cancer to predict the efficacy of chemotherapy and subsequent relapse, essentially due to the poor sensitivity of ctDNA detection.

Highlights

Gastric cancer displays significant global variation in incidence, with the highest rates observed in Eastern Asia, Eastern Europe and South America [1]
We report that circulating tumor DNA (ctDNA) can detected by customized droplet digital PCR (ddPCR) assays in 20% of nonmetastatic gastric cancer patients prior to the initiation of preoperative chemotherapy
CtDNA was detectable in one patient (n = 1/13, 95% CI = 1%–33%) with an mutant allele frequency (MAF) of 0.7%

Summary

Introduction

Gastric cancer displays significant global variation in incidence, with the highest rates observed in Eastern Asia, Eastern Europe and South America [1]. Current treatment guidelines recommend that chemotherapy should be administered for 2–4 months prior to surgery, and resumed thereafter, for a total of about 6 months of chemotherapy [3,4]. Despite this combined treatment, the long-term survival of non-metastatic gastric cancer remains limited, with a 36% 5-year overall survival rate [2]. While the pathological response to preoperative chemotherapy has been associated with relapse-free and overall survival [5], no biological or imaging tool is able to detect and quantify minimal residual disease, i.e., residual cancer cells after chemotherapy and/or surgery that are responsible for subsequent metastatic relapse. Circulating tumor biomarkers have demonstrated their clinical validity in several non-metastatic cancer types either as baseline prognostic biomarkers, as a monitoring tool during preoperative chemotherapy and/or as a way to detect minimal residual disease [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]

Methods

Results

Conclusion