Liquid biopsies have recently been introduced as a diagnostic method from blood samples for detection of molecular biomarkers without the need of invasive procedures. Circulating tumor cells (CTC) or pieces of DNA from tumor cells that are circulating in the blood (circulating free DNA or cfDNA) can be found in cancer patients. CTCs and cfDNA analyses have provided independent information on prognosis in early and advanced stages of cancer.
Liquid biopsies can be used to obtain insights into the biology of metastasis or as companion diagnostics for a better understanding of therapy-induced selection of cancer cells, thus improving the stratification of therapies for patients. The challenge in CTC isolation is their rarity in blood and sophisticated methods for CTC isolation have been developed. Monitoring of CTCs before, during and after systemic therapy has provided unique information for the clinical management of the patient.
In addition to CTC, liquid biopsies are now being developed for detection of various types of rare circulating single cells such as Pathogenic Immune Cells (PIC) or circulating Fetal Cells (CFC) for prenatal diagnosis.