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Mucins are large and complex glycoproteins that are expressed by several epithelial tissues. Mucins have been grouped into 7 distinct families, MUC-1 though MUC-7, based on their genetic and biochemical characteristics. MUC-1 mucins are expressed at the luminal surface of glandular cells. In malignant cells, this mucin is over-expressed and increased amounts are shed into the circulation. Monoclonal antibodies that recognize distinct epitopes on this molecule have been used to develop immunoassays that quantitate MUC-1 mucin levels in serum. Clinically, these immunoassays have been used to monitor breast cancer recurrence. The first assay available was CA15.3. In the past 2 years, CA 15.3 has been largely replaced by CA27.29, which uses a different set of monoclonal antibodies to measure the same mucin molecule. The CA27.29 assay has almost the same performance characteristics as CA 15.3 for monitoring breast cancer. Either assay detects recurrent disease in approximately 50% of asymptomatic patients who eventually relapse approximately 6 months before it becomes clinically evident. Measurements of CA 27.29 in women with treated carcinoma of the breast may be useful for predicting early recurrence of disease. The Food and Drug Administration has approved CA 27.29 for serial testing in women with prior stage II or III breast cancer who are clinically free of disease. The reference range is 0 - 38 U/mL. Increased levels of CA 27.29 (>38 U/mL) may indicate recurrent disease in a woman with treated breast carcinoma and may be useful as an indication that additional tests or procedures should be performed to confirm recurrence. CA 27.29 is not a specific marker for breast cancer. Malignancies involving the stomach, colon, lung, pancreas, ovary, liver and uterus can also produce elevated concentrations. Up to one fourth of patients with cirrhosis and renal failure also have elevated CA 27.29 levels. Sensitivity is too low for CA 27.29 to be used as a screening or diagnostic test for breast cancer. |
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