Why are carcinoembryonic antigen (CEA) levels higher in right-sided colon cancer than in left-sided colon cancer?

CEA Levels in Right-Sided vs. Left-Sided Colorectal Cancer

The evidence does not support that CEA levels are consistently higher in right-sided colon cancer compared to left-sided colon cancer. Based on the available guidelines and research, there is no clear documentation of a difference in carcinoembryonic antigen (CEA) levels between right-sided and left-sided colorectal cancers.

CEA Production and Clinical Significance

• CEA is produced by approximately 90% of colorectal cancers and contributes to the malignant characteristics of tumors 1
• CEA is a complex glycoprotein that can be measured quantitatively in serum and serves as a tumor marker for colorectal cancer 1
• The specificity of CEA for identifying colorectal cancers is high, but the sensitivity is very low, making it unsuitable for population screening 2

Factors Affecting CEA Levels

• CEA levels are influenced by multiple factors beyond tumor location:
  • The CEA production capacity of cancer cells 3
  • The ability of surrounding tissue to release CEA into the bloodstream 3
  • Tumor stage and burden 2
  • Non-cancer related conditions such as gastritis, peptic ulcer disease, diverticulitis, liver diseases, COPD, diabetes, and inflammatory states 2

CEA and Tumor Location

• Current ASCO guidelines on tumor markers in gastrointestinal cancer do not indicate a difference in CEA levels based on tumor location (right-sided vs. left-sided) 2
• A 2020 study examining the association between CEA ratio, tumor location, and overall survival found no significant difference in CEA patterns between right-sided and left-sided tumors 4
• The immunohistochemical staining status of CEA in metastatic tissue appears to be more closely related to serum CEA levels than primary tumor location 3

Clinical Patterns of CEA Elevation

• Two distinct patterns of CEA rise have been observed in recurrent colorectal cancer:
  • A "fast" rise where serum concentrations reach high levels quickly (within 6 months)
  • A "slow" rise where concentrations remain lower for at least 12 months 5
• These patterns correlate more with the type of recurrence (metastatic vs. local) rather than the original tumor location 5

CEA in Clinical Practice

• Preoperative CEA is an important independent prognostic variable in predicting outcomes 2
• Elevated preoperative CEA (≥5 ng/mL) correlates with poorer prognosis regardless of tumor location 2, 1
• Postoperative CEA monitoring is recommended every 3 months for patients with stage II or III disease for at least 3 years after diagnosis 2
• CEA is the marker of choice for monitoring metastatic colorectal cancer during systemic therapy 2

Important Clinical Considerations

• CEA surveillance may detect potentially resectable metastases, but the test is neither absolutely sensitive nor specific for recurrent cancer 6
• Some patients may exhibit very subtle increases in CEA levels that still indicate recurrence, even when values remain within the normal range 6
• The perioperative CEA ratio (post-op/pre-op CEA) may be a more significant prognostic factor than absolute CEA values or tumor location 4

In conclusion, while there are documented differences between right-sided and left-sided colorectal cancers in terms of incidence, clinical presentation, molecular pathogenesis, and outcomes, current evidence does not support a consistent difference in CEA levels based on tumor location alone.