Table 2.

Merits and Demerits of CTC-based methods, clinical methods and other biomarkers

Methods		Merits	Demerits
CTCs	Immunoaffinity-based	Capture cells of specific phenotypes with relatively high specificity, high purity; Overcome the heterogeneity of physical characteristic	Lack of broad-spectrum specific biomarkers; Affect cell viability, downstream phenotype identification and molecular analysis; High cost, low throughput
	Biophysical Properties-based	Good cell integrity and viability; Not restricted by cell surface markers; Low cost, high throughput	Low specificity and purity; Significant difference in cell size lead to the omission of small CTTs
	Commonality	Low-risk, Low-invasive method for continuous sample acquisition; Real-time (earlydiagnosis, predict metastasis or recurrence, monitor treatment response); Live cells, morphological and molecular characterization (precision medicine); In vitro culture, drug resistance and drug sensitivity cell experiments	Targeted cells are scarce; Technical limitations (sensitivity and specificity); Lack of uniform standards (cut-off value, detection time, etc.) Heterogeneity; Lack of large-scale prospective trials
Clinical Methods	Medical imaging	Mature, standardized; Non-invasive, dynamically monitor the morphological changes of lesions;	Insufficient sensitivity; Not in-time; The nature of some lesions is not clear
	Pathological	Mature, standardized; High accuracy; Immunohistochemical staining, genetic testing, in vitro cell culture, etc.	Invasive injury (local reaction, infection, dissemination and metastasis, etc.); Some patients cannot undergo tissue biopsy (location, size, general condition, etc.); Heterogeneity (time and space)
	Tumor biomarkers	Easy access to samples; Dynamic monitoring of tumor changes and treatment response	High false positive and false negative rate; Poor specificity
Other biomarkers	ctDNA	Relatively mature technologies (compared with CTCs); Short half-life time; More sensitive to tumor status; Comprehensive molecular information of tumor	DNA fragments from necrotic or apoptotic cells, cannot represent living tumor cells; Only provide genetic information; Low gene mutation abundance, poor sensitivity
	Extracellular Vesicles	Large quantity, easy to enrich (compared with CTCs); Extracellular vesicles can prevent internal nucleic acid substances from being degraded, high stability	Immature technologies (isolation, purification, enrichment of internal specific markers, etc.)
	microRNA	Closely related to cell metabolism under physiological and pathological conditions	Immature technologies, few related research