Table 2.

Studies evaluating circulating tumor DNA for minimal residual disease

Ref.	Title	Clinical relevance
Alcaide et al[73], 2020	Evaluating the quantity, quality and size distribution of cell-free DNA by multiplex droplet digital PCR	Presents a novel droplet digital PCR assay to identify suboptimal samples and aberrant cfDNA size distributions, the latter typically associated with high ctDNA levels
King et al[76], 2023	Prospectivelongitudinal tumor-informed ctDNA in resectable biliary tract cancers	Assesses the utility of ctDNA levels in evaluating response in the absence of radiographically visible disease. ctDNA showed a higher detection rate than CA 19-9 prior to resection
Park et al[77], 2024	Ultrashort cell-free DNA fragments and vimentin-positive circulating tumor cells for predicting early recurrence in patients with biliary tract cancer	Investigates the effectiveness of cell-free DNA and circulating tumor cells in predicting early recurrence after curative surgery and adjuvant therapy in patients with BTC
Yoo et al[78], 2024	Circulating tumor DNA status and dynamics predict recurrence in patients with resected extrahepatic cholangiocarcinoma	Evaluates superiority of ctDNA over conventional biomarkers in predicting recurrence and informing adjuvant chemotherapy in resected extrahepatic cholangiocarcinoma
Yu et al[79], 2025	Detecting early recurrence with circulating tumor DNA in stage I-III biliary tract cancer after curative resection	Evaluates serial ctDNA testing for surveillance after curative resection in early-stage BTC. Identified recurrence in 93.8% of cases, with a median lead time of 3.7 months

BTC: Biliary tract cancer; cfDNA: Cell free DNA; ctDNA: Circulating tumor DNA.