A 65 year-old patient with adenocarcinoma of the colon in remission presents for follow-up. Which of the following tumor markers should be monitored?

• A. AFP
• B. CEA
• C. CA 19-9
• D. CA-125

Answer: (B)

Monitoring tumor markers after surgical management of colorectal cancer relies on a marker that tends to reflect tumor burden in this disease. Carcinoembryonic antigen (CEA) fits this role because many colon cancers produce CEA, and its levels usually rise when the cancer recurs or metastatic disease develops. In follow-up, serial CEA measurements are used to watch for changes over time: a rising or persistently elevated CEA raises concern for recurrence and typically leads to further imaging to locate any recurrent disease. Conversely, stable or falling CEA levels suggest no evidence of active disease. It’s important to remember that CEA isn’t perfect—it isn’t produced by all colorectal cancers, and levels can be influenced by factors like smoking or inflammatory conditions—so it’s interpreted with clinical context and alongside imaging.

The other markers cited are not standard for colorectal cancer surveillance: AFP is more associated with hepatocellular carcinoma and certain germ cell tumors, CA 19-9 is linked to pancreatic and biliary cancers, and CA-125 is used for ovarian cancer.