Table 2.

Studies evaluating the clinical utility of circulating tumor DNA (ctDNA) in patients with advanced biliary tract cancer (BTC).

Study	Patient Population	n	ctDNA Assay	Study Design	Mutations Tested in the Plasma	Major Findings
Andersen et al. [37]	CCA	5	Multiplex digital PCR	Plasma samples from CCA patients with known tumor mutations were tested to determine blood/tissue concordance	Total 31 mutations in the KRAS, NRAS, BRAF, and PIK3CA genes.	All known mutations in the tumor were detected in plasma samples in all patients.
Ettrich et al. [36]	CCA (54% iCCA, 46% eCCA)	24	NGS-based assay	Tumor tissue and corresponding plasma samples were collected to investigate blood/tissue concordance	15 genes frequently mutated in CCA *	The blood/tissue concordance was 74% overall and 92% for intrahepatic CCA. The VAF in ctDNA correlated with the tumor burden, and in iCCA, with the PFS.
Goyal et al. [38]	Phase I study of BGJ398 in iCCA patients	3	Droplet digital PCR	ctDNA analyses on serial plasma samples before and after treatment to determine the resistance mechanism	FGFR2 mutations	In all 3 cases, post-progression sequencing of the FGFR2 gene demonstrated de novo point mutations that conferred resistance to BGJ298
Mody et al. [39]	Advanced BTC (70% iCCA)	124	NGS-based assay developed by Guardant Health	Plasma samples obtained to find therapeutically relevant alterations as part of routine clinical care	73-gene panel	Therapeutically relevant alterations were observed in 55% of patients (21% of patients had one of the following alterations—BRAF mutations, ERBB2 amplification, FGFR2 fusions, FGFR2 mutations, and IDH1 mutations).

Abbreviations: CCA, cholangiocarcinoma; PCR, polymerase chain reaction; iCCA, intrahepatic cholangiocarcinoma; eCCA, extrahepatic cholangiocarcinoma; VAF, variant allele fraction; PFS, progression-free survival; NGS, next-generation sequencing.* TP53, KRAS, ARID1A, BAP1, PBRM1, PIK3CA, SMAD4, FBXW7, IDH1, BCL2, BRAF, CDKN2A, ERBB2, IDH2, and NRAS.