Many clinicians have elected to incorporate these ctDNA-based assays in the surveillance of resected colorectal cancer, despite limited supportive clinical data.11,12,13,14,15 The enthusiasm around these assays, particularly Signatera, was generated by a large observational surveillance trial11 that evaluated CEA levels, CT imaging, and ctDNA in patients with stage I to III colorectal cancer. Here, CEACAM5 is linked to colorectal cancer.