Recent Advances in Methods for Circulating Tumor Cell Detection

Abstract

Circulating tumor cells (CTCs) are released from primary tumors and transported through the body via blood or lymphatic vessels before settling to form micrometastases under suitable conditions. Accordingly, several studies have identified CTCs as a negative prognostic factor for survival in many types of cancer. CTCs also reflect the current heterogeneity and genetic and biological state of tumors; so, their study can provide valuable insights into tumor progression, cell senescence, and cancer dormancy. Diverse methods with differing specificity, utility, costs, and sensitivity have been developed for isolating and characterizing CTCs. Additionally, novel techniques with the potential to overcome the limitations of existing ones are being developed. This primary literature review describes the current and emerging methods for enriching, detecting, isolating, and characterizing CTCs.

Keywords: characterization; circulating tumor cells; detection; enrichment; microfluidic.

Figure 1

Schematic depiction of an ISET-based system for CTC enrichment. The filtration device, whose components are shown in (A), is used to collect blood (B), which is filtered through a membrane (C). The auxiliary components are then removed to enable further analysis of the membrane-bound CTCs (D) (polymerase chain reaction, PCR; next-generation sequencing, NGS).

Figure 2

The dielectrophoretic field-flow fractionation (DEP-FFF) method allows CTCs to be isolated from blood samples (A) by separation in a dielectrophoretic chamber (B) under the influence of hydrodynamic lift and levitation forces (↑), gravitational and sedimentation forces (↓), and the fluid velocity (→).

Figure 3

The magnetic-activated cell sorting (MACS) system uses antibody-coated magnetic beads to capture CTCs (A). The separator’s magnetic field causes labeled cells to be retained on the column while unlabeled cells pass through unimpeded (B), after which the labeled CTCs are released (C).

Figure 4

Herringbone chips (HB chips) capture CTCs directly from whole blood (A) in herringbone-etched microchannels, differentiating them from blood cells based on their size and mobility. Captured cells can be directly stained and enumerated (B) on the chip using conjugated antibodies and/or (C) washed out from the chip for further analysis (polymerase chain reaction, PCR; next-generation sequencing, NGS).

Figure 5

The TetherChip CTC capture system relies on the high affinity of CTC microtentacles for a crosslinked polyelectrolyte multilayer formed by thermal imidization.

Figure 6

Operating principles of the GILUPI CellCollector for in vivo CTC enrichment on a functionalized surface. CTCs are captured by antibodies immobilized on a hydrogel and can be released from the surface for analysis after removing the cannula from the vein.