However, unlike CEA, wherein measurable levels can be found in normal individuals but a proportion of colorectal tumors can be non-secretors of CEA, ctDNA as a measure of minimal residual disease (MRD) is a binary metric whose presence indicates that a large burden of residual metastatic cancer cells remain in one's body (13). The gene discussed is CEACAM5; the disease is metastatic malignant neoplasm.