Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (791 page)

   Limitations

   When an abnormal level is found, the test should be repeated. If confirmed, the patient should undergo imaging of potential reoccurrence sites.

   Same methodology should be used to monitor an individual patient. A significant change in plasma concentration is +25%.

   After complete removal of colon cancer, CEA should fall to normal in 6–12 weeks. Failure to decline to normal concentrations postoperatively suggests incomplete resection. Immunohistochemistry of resected specimen is used to identify 20% of these cancers that do not express CEA for whom monitoring is misleading. In such cases, may use serum ALP and diagnostic imaging.

   Prognosis is related to serum concentration at time of diagnosis (stage of disease and likelihood of recurrence). CEA concentrations <5 ng/mL before therapy suggest localized disease and a favorable prognosis, but a concentration >10 ng/mL suggests extensive disease and a poor prognosis; >80% of colon carcinoma patients with values >20 ng/mL have recurrence within 14 months after surgery. Plasma CEA >20 ng/mL correlates with tumor volume in breast and colon cancer and is usually associated with metastatic disease or with a few types of cancer (e.g., cancer of the colon or pancreas); however, metastases may occur with concentrations <20 ng/mL. Values <2.5 ng/mL do not rule out primary, metastatic, or recurrent cancer. Increased values in node-negative colon cancer may identify poorer-risk patients who may benefit from chemotherapy.

   Patterns of CEA change during chemotherapy.

   Uninterrupted increase indicating failure to respond.

   Decrease indicating response to therapy.

   Surge in CEA for weeks followed by a decrease indicating response.

   Immediate, sustained decrease followed by an increase indicating lack of response to therapy.

   Significant is 25–35% change from baseline of equal or increased values during the first 2 months of therapy.

   Survival is significantly longer if titer decreases below this baseline.