Table 2.

Summary of the studies performed in GIST patients and included in the review.

Author, year	Aim	Patients		Technique	Result
		N of tumor samples	N of plasma samples
Demetri and colleagues90	To consider circulating DNA in plasma as a source of tumor DNA.	102 tissue	163	Sanger sequencing (tissue) and BEAMing (plasma)	Demonstrated utility of plasma-based circulating DNA analysis of target oncogenes.
Maier and colleagues92	To detect tumor DNA carrying KIT or PDGFRA mutation in plasma and correlate its discovery with the disease clinical course.	FFPE from 38 GISTs	291 (from 38 GISTs)	Allele-specific L-PCR assay	- Confirmed presence of KIT/PDGFRA mutant cfDNA. - The amount of mutant cfDNA correlates with the disease clinical course, being significantly higher in patients with active disease compared with those in complete remission.
Yoo and colleagues93	To assess the relevance of soluble serum proteins and ctDNA as biomarkers for TKI-refractory GISTs.	Archival tissue from 28 GIST	58 (from 30 GISTs: n = 30 day 1 of cycle 1; n = 28 day 1 of cycle 2)	BEAMing	Demonstrated usefulness of serum ctDNA for the identification of TKI-resistant mutations.
Bauer and colleagues94	To evaluate plasma sequencing to detect or monitor the spectrum of resistance mutations in GISTs.	Tumor tissue from 15 GISTs	30 (from 22 GISTs)	Illumina MiSeq platform	Showed that plasma sequencing detects a multitude of resistance mutation in KIT and other genes.
Kang and colleagues95	To analyze ctDNA from the plasma of GIST patients on TKI therapy.	Tumor tissue from 3 GISTs	Not specified (from 3 GISTs)	NGS	- Demonstrated detection of primary and secondary mutations in ctDNA. - Resistant mutations in ctDNA may represent early biomarkers for treatment response.
Wada and colleagues96	To investigate if secondary KIT mutations can be detected in ctDNA.	Primary tumor and imatinib-resistant lesion from 4 GISTs	8 (from 4 GISTs: samples taken before and after the treatment of imatinib-resistant lesions with sunitinib)	NGS	- Confirmed detection of KIT secondary mutation in ctDNA. - Secondary mutation in plasma were the same identified in imatinib-resistant tumor tissue. - The fraction of ctDNA changed along with tumor status.
Kang and colleagues97	To validate the use of ctDNA as a biomarker for determining KIT and PDGFRA mutations.	FFPE from 25 GISTs	25 (from 25 GISTs, taken before surgery)	Sanger sequencing (tissue), NGS (tissue and plasma)	Demonstrated the feasibility of using ctDNA as a surrogate tissue for the presence of KIT/PDGFRA mutations prior to resection of primary tumor.
Boonstra and colleagues98	To develop a ddPCR assay to detect common KIT exon 11 mutations in both tumor tissue and ctDNA.	Archival FFPE from 27 GISTs	22 (from 22 GIST, taken before start of TKI treatment)	Sanger sequencing (FFPE), NGS (FFPE), ddPCR (FFPE and plasma)	Demonstrated the feasibility of a single ddPCR assay for the detection of multiple KIT exon 11 mutations in ctDNA.
Namløs and colleagues99	To detect KIT and PDGFRA mutations with high sensitivity in ctDNA from patients with GISTs through NGS.	Tissue from 50 GIST	44 blood samples from treatment-naïve patients and 6 from GISTs under TKIs	NGS (tissue and plasma)	- Plasma from high-risk patients or with metastatic disease showed more frequently detectable mutations in ctDNA compared with patients with localized or intermediate to low-risk GISTs. - Detection of ctDNA in patients undergoing TKI treatment can be related to the disease development.
Li and colleagues100	To investigate feasibility of detecting ANO1 in CTCs in GISTs and association between ANO1 expression and clinical outcome of GIST.		Blood samples from 121 GISTs (of whom, 52 were high-risk GISTs, 42 intermediate risk, 18 low or very low risk), 21 gastric cancer, 23 colorectal cancer patients and 10 healthy controls	qRT-PCR	- ANO1 is a specific marker of CTCs in GISTs -High ANO1 correlated with high risk, large tumor size and high mitotic count - ANO1 positive expression correlated with poor disease-free survival. - In the neoadjuvant setting, reduction of ANO1 expression correlated with the response to imatinib.
Atay and colleagues101	To provide a comprehensive proteome analysis and characterization of GIST-derived exosomes that might be used as a resource for the discovery of new diagnostic biomarkers and therapeutic targets.		30 (from 18 GISTs and 12 healthy donors)	Mass spectrometry	Showed proteomic analysis of circulating exosomes is suitable for diagnosis, prognosis and monitoring of treatment response.

BEAMing: bead emulsion amplification and magnetics; cfDNA: circulating free DNA; ctDNA: circulating tumor DNA; ddPCR: digital droplet PCR; FFPE: formalin-fixed paraffin-embedded; GIST, gastrointestinal stromal tumor; PCR, polymerase chain reaction; qRT-PCR: quantitative-real-time reverse transcription PCR; NGS: next-generation sequencing; TKI, tyrosine-kinase inhibitor.