Breast cancer stem cells and circulating tumor cells: Dual drivers of progression and relapse

Table 2 Circulating tumor cell detection methods: Types, principles, and key features

Method type	Detection principle	Technologies	Advantages	Limitations
Label-dependent	Antigen-based (surface markers)	CellSearch® (EpCAM+). HER2, CD45-based	FDA-approved. High specificity for epithelial CTCs	Misses EMT/mesenchymal CTCs. Marker heterogeneity limits sensitivity
Label-independent	Physical properties: Size, density, deformability	Parsortix®. Filtration. Microfluidics	Captures broader CTC spectrum. Detects EMT-like CTCs	Lower specificity. Overlap with normal blood cells
Combination methods	Antigen + physical property integration	Microfluidic chips with antibodies	Improved sensitivity and specificity. Better for rare subtypes	More complex and costly
CTC cluster detection	Enrichment of tumor cell aggregates	Size-based filters. Inertial focusing	Important for early metastasis. Reflects high aggressiveness	Rare and fragile. Difficult to preserve integrity during handling
Single-cell analysis	High-resolution detection of individual CTCs	DEPArray. RareCyte. MCA/gel-based	Enables genomic/proteomic profiling. Detects rare variants	Low throughput. Requires optimization and high cost

FDA: Food and Drug Administration; CTC: Circulating tumor cell; EpCAM: Epithelial cell adhesion molecule; HER2: Human epidermal growth factor receptor 2; EMT: Epithelial-mesenchymal transition; MCA: Microcavity array.