Imagine if doctors could diagnose cancer, follow disease progression and monitor treatment results all through a simple blood test. No more subjecting patients to painful biopsies; no more using those biopsies to make treatment decisions years down the road. That is the tantalizing promise of liquid biopsies. Unlike traditional biopsies, which take a sample of tissue that—hopefully—includes cancer cells, liquid biopsies screen for free-floating pieces of DNA or RNA from the cancerous cells.
These extracellular DNAs and RNAs, called circulating cell-free nucleic acids (ccfNA), were first observed in human blood in 1948. Although these snippets of biological information come from a number of sources including normal cell death events, an elevated concentration of ccfNA can be associated with different diseases. In the 1970s, researchers reported that the ccfDNA concentration in serum samples of individuals with breast cancer was elevated and that the concentration varied, depending upon disease progression and treatment (1) . These results were followed by research in the 1980s and 1990s that correlated the presence of ccfDNA in serum samples to malignancy of disease (2) and then further identified mutated Ras molecules in serum samples taken from pancreatic cancer patients (3) (4) .
During development, tumor cells release their DNA into the blood circulation through apoptotic and necrotic cell death events as well as secretion from live cells. These events result in relatively high levels of ccfDNA in the blood of cancer patients. It also means that this population of circulating fragments found in a patient’s blood could act as biomarkers for their disease.