By Anna Quinlan and Dawne Shelton
Disease-associated mutations, especially those linked to cancer, can be prognostic of outcome and inform treatment choices. Traditional tissue biopsies, however, limit our ability to implement such personalized treatments. These invasive surgical procedures can be used to genotype a tumor prior to treatment, but they are not amenable to serial tracking of treatment efficacy or disease progression. Furthermore, for some cancers, such as metastatic breast or prostate cancer, or for tumors that are not easily accessible, tissue biopsies can prove impossible.
By using cell-free DNA (cfDNA) to quantify cancer markers in blood or other bodily fluids, liquid biopsies can eliminate the need for invasive surgical procedures. However, the most commonly used approaches to quantify cfDNA, next-generation sequencing (NGS) and quantitative real-time PCR (RT-qPCR), have their own challenges.