Role of liquid biopsies in colorectal cancer

Colorectal cancer (CRC) is the third most common cancer worldwide, with a global incidence of over 1 million cases. In the era of personalized medicine, tumor sampling is essential for characterizing the molecular profile of individual tumors. This provides pivotal information regarding optimal sequencing of therapy and emergence of drug resistance, allowing for timely therapy adjustment. However, tumor tissue sampling offers static information in a single time point and area of disease at the time of biopsy, which may not entirely represent the heterogeneity of molecular alterations. Moreover, tumor biopsies often involve invasive procedures with potential risks to patients. Less invasive, safer, and real-time methods such as liquid biopsies have generated increasing interest as a surrogate of solid tumor biopsies. Liquid biopsy allows for noninvasive survey with detection of cell-free circulating tumor DNA (ctDNA) or circulating tumor cells. Blood-based assays are the most widely studied. Additionally, the quantity of ctDNA detected has been shown to correlate with tumor burden and enables assessment of tumor heterogeneity. In this article, we discuss the concept of liquid biopsies including ctDNA and circulating tumor cell, and their current application in the diagnosis and management of CRC. We suggest that liquid biopsies can be successfully used to characterize the molecular profile of CRC, monitor disease, detect minimal residual disease after surgery, and identify therapeutic targets and mechanisms of drug resistance. This strategy could potentially imply an early change in treatment, sparing unnecessary side effects, and minimizing health costs. Combined radiological and liquid biopsy assessments will likely become more standard in CRC oncology. However, large prospective studies are needed to definitively establish the role of liquid biopsy.