What cancer markers are used for colorectal (bowel) cancer?

Cancer Markers for Bowel Cancer

Carcinoembryonic antigen (CEA) is the primary and most clinically useful tumor marker for colorectal cancer management, though it should NOT be used for screening or diagnosis. 1

Primary Tumor Marker: CEA

CEA is the marker of choice for colorectal cancer and has specific evidence-based applications 1:

Clinical Uses of CEA:

Preoperative Staging:

• May be ordered before surgery if it assists in staging and surgical planning
• Elevated preoperative CEA (≥5 ng/mL) correlates with poorer prognosis
• However, insufficient data to use CEA for deciding adjuvant therapy 1

Postoperative Surveillance:

• Perform CEA testing every 3 months for at least 3 years in stage II or III disease patients who are candidates for surgery or systemic therapy
• An elevated CEA (if confirmed by retesting) warrants further evaluation for metastatic disease
• Wait until chemotherapy is finished before initiating CEA surveillance, as chemotherapy can falsely elevate levels 1

Monitoring Metastatic Disease:

• CEA is the marker of choice for monitoring response to systemic therapy in metastatic colorectal cancer
• Measure at treatment start and every 1-3 months during active treatment
• Persistently rising values suggest progressive disease even without radiographic confirmation
• Caution: Spurious early rises may occur during the first 4-6 weeks of new therapy, especially with oxaliplatin 1

Important CEA Limitations:

• NOT recommended for screening - lacks sensitivity and specificity 1
• NOT recommended for diagnosis 1
• Non-cancer causes of elevation include: gastritis, peptic ulcer disease, diverticulitis, liver diseases, COPD, diabetes, and any inflammatory state 1

Molecular Biomarkers (For Treatment Selection, NOT Screening)

RAS Mutational Testing:

• Must be performed in patients being considered for anti-EGFR therapy
• Test KRAS and NRAS codons 12,13 (exon 2); 59,61 (exon 3); and 117,146 (exon 4) - "expanded RAS" 2

BRAF p.V600 Testing:

• Should be performed for prognostic stratification
• Should be performed in deficient MMR tumors with loss of MLH1 to evaluate Lynch Syndrome risk 2

Markers NOT Recommended for Routine Clinical Use

The following have insufficient evidence for routine clinical application 1:

• CA 19-9 - not recommended for screening, diagnosis, staging, surveillance, or monitoring
• p53 expression or mutation
• ras oncogene (for screening/surveillance purposes)
• DNA ploidy or flow cytometric proliferation analysis
• Thymidine synthase (TS), dihydropyrimidine dehydrogenase (DPD), thymidine phosphorylase (TP)
• Microsatellite instability (MSI) - not for prognosis or predicting fluorouracil response
• 18q loss of heterozygosity or DCC protein

Emerging Blood-Based Markers (Research Stage)

While promising, these are not yet ready for routine clinical use 3, 4:

• Methylated SEPT9 DNA - most studied but shows high variability (sensitivity 48-96%, specificity 80-99%)
• Methylated SDC2 DNA
• Circulating tumor DNA (ctDNA) - promising for post-treatment surveillance and recurrence prediction
• MicroRNAs - various panels under investigation
• Multi-marker panels combining CEA, anti-p53, osteopontin, seprase, and ferritin

Common Pitfalls to Avoid:

1. Do not use CEA alone to initiate systemic therapy - always confirm with imaging 1
2. Do not interpret rising CEA during first 4-6 weeks of new therapy as progression - wait for confirmation 1
3. Do not use the same markers for screening that are used for surveillance - CEA has no role in screening 1
4. Ensure all CEA tests for a given patient are performed in the same laboratory using the same technique 5