CEACAM5 and colorectal cancer: Colorectal cancer (CRC)is the third most common malignancy andthe second leading cause of cancer death globally,1 with 1.8 million new cases diagnosed in 2018.2 First discovered by Gold and Freedman3 in 1965, carcinoembryonic antigen (CEA) is anantigen produced by many human tumors, including breast, lung, andcolorectal cancer.4 Multiple studies havelinked raised CEA levels to poor disease prognosis.5−9 As CEA is upregulated in ∼90% of advancedCRC,10 routine CEA blood tests are takenafter curative-intent surgery, with 3–7 ng/mL11 usually prompting further investigation.