A Prospective Study Utilizing Circulating Cell Free DNA (cfDNA) Use in the Detection of RAS Mutations in Patients With Advanced Colorectal Cancer.

Colorectal cancer remains the commonest cancer among men, and third commonest among women in Saudi Arabia . Presentation with metastatic disease occurs in almost one third of patients , with 5-year survival decreasing significantly from 90% in stage 1 to 14% once the disease is metastatic . There is enthusiasm in the potential for liquid biopsies to provide easily accessible genetic biomarkers for mutational cancer characterization . Epidermal growth factor receptor (EGFR) monoclonal antibodies are widely used in the treatment of advanced colorectal cancer that do not harbor RAS mutations (RAS wild type). Hence genotyping of oncogenic RAS mutations is essential prior to the initiation of systemic therapy for such patients as the presence of these mutations predict resistance to EGFR targeted antibodies such as Cetuximab and Panitumumab . Detection of such mutations has been done on tissue biopsies with the disadvantage of this being an invasive procedure, and data suggesting that such testing may not be reflective of the true mutational burden of the disease since a single fragment of tissue may be inadequate to reflect the intratumoral heterogeneity. There is increasing evidence suggesting that liquid biopsies or blood based mutational profiling can provide a more comprehensive molecular profile of the disease, and carries the advantage of being minimally invasive. Serial liquid biopsies can act as a tool to identify spatial and temporal heterogeneity predicting response or resistance to targeted agents, and can shed light into the emergence (or disappearance) of specific mutations that may potentially be targeted with newer anti cancer agents . Circulating cell free DNA (cfDNA) consists of small nucleic acid fragments liberated from cells by rupture, necrosis or apoptosis, and is now increasingly being used to detect RAS (and other) mutations in patients with advanced colorectal cancers. KRAS has remained an "undruggable" target for decades until the most recent