CEACAM5 and colorectal carcinoma: In an LS174T CRC xenograft model, mass-encoded synthetic biomarkers detect 130 mm tumours3, whereas circulating tumour DNA (ctDNA) can detect tumour sizes of >1,000 mm3, and carcinoembryonic antigen detection has a threshold of 135–330 mm3 (refs. 4,7,24).