Aadel Chaudhuri, MD, PhD, Washington University School of Medicine, St. Louis, USA, discusses what research still needs to be done into using ctDNA as a biomarker for minimal residual disease (MRD) post-surgery for patients with solid tumors. Dr Chaudhuri also compares prognostic and predictive biomarkers. This interview took place at the International Society of Liquid Biopsy (ISLB) 2021 Virtual Meeting.