Fig. 2.

Liquid biopsies. (A) Cerebrospinal fluid contains both cellular and acellular material. (B) Centrifugation isolates cells for circulating tumor cell (CTC) analyses. Antibodies against cancer cell surface markers conjugated with ferromagnetic particles enable isolation of cancer cells. These cells are further detected with fluorescently conjugated antibodies as part of the CellSearch system. Alternatively, cells may be stained with fluorescently conjugated antibodies against a variety of cell surface markers and enumerated using flow cytometry. (C) Acellular material contains extracellular DNA (ctDNA). After isolation by ultracentrifugation, and library preparation, this DNA can be amplified and subjected to analysis of a single locus (PCR), or entire exomes, genes, or genomes.