Benjamin Besse, MD, PhD, of the Gustave Roussy Institute, Villejuif, France, discusses the value of liquid biopsy in detecting RET fusions/mutations in patients with non-small cell lung cancer (NSCLC) and medullary thyroid cancer (MTC), at the European Society for Medical Oncology (ESMO) 2018 Congress, in Munich, Germany. Liquid biopsy may not only inform the use of RET-inhibitor treatments like LOXO-292, but also aid monitoring of drug efficacy and even emergence of treatment resistance.