(i) Antibody (Ab)-coated MPs are injected to immunomagnetically label rare analytes in the blood; in this case, CTCs. (ii) The flexible MagWIRE, composed of magnetic units with alternating polarity, is introduced through an intravenous catheter to collect and enrich MP-bound cells on the wire as the entire blood volume circulates past (approximately over 1 h). In principle, the patient could move freely after MP injection and MagWIRE placement, and return 1 h later for its removal. (iii) The MagWIRE is removed from the vein and the magnets are displaced from their biocompatible plastic sheath, leaving the captured cells on the sheath for elution, ex vivo cell culture and downstream molecular analysis. RBC, red blood cell. Ct, threshold cycle.