Daniel V. Catenacci, MD, of the University of Chicago Medical Center, Chicago, IL, discusses the results of a study evaluating personalized, neoantigen-directed immunotherapy in solid tumors. This novel approach involved the sequencing of patient’s tumors and identification of optimal mutations. The Phase I/II study included patients with microsatellite stable colorectal cancer (MSS-CRC), gastroesophageal cancer (GEA) or non-small cell lung cancer (NSCLC). A dose-escalation trial was conducted and circulating DNA dynamics over time were observed. Of the 22 evaluable patients, one complete response was observed as well as five patients with stable disease. In MSS-CRC, 44% of patients reported a drop of ctDNA as their best response which correlated with target shrinkage and longer-term progression-free survival. This interview took place during the European Society for Medical Oncology (ESMO) 2021 congress.