Breast Cancer Tumor Markers (CEA and CA 15-3)

The Breast Cancer Tumor Markers (CEA and CA 15-3) panel is used to support prognostic assessment, to aid earlier recognition of recurrence and distant metastases, and to monitor response to therapy. Marker kinetics are particularly informative when anatomic response criteria are difficult to apply, including malignant effusions or predominantly lytic bone disease. Common synonyms include carcinoembryonic antigen (CEACAM5/CD66e) and CA 15-3, the MUC1 soluble form. This testing is not recommended for screening or for establishing a primary diagnosis of breast cancer due to suboptimal sensitivity and specificity. Results are interpreted together with clinical evaluation and imaging findings.

CEA is a large glycoprotein involved in cell adhesion. Serum CEA may be elevated in diverse malignancies—breast, colorectal, pancreatic, gastric, lung, medullary thyroid, bladder, renal, and prostate—as well as in several benign conditions, which limits specificity. CA 15-3 is a soluble fragment of the transmembrane mucin MUC1; its sensitivity correlates with stage in breast cancer, and it has limited utility in early-stage disease. When followed serially, rising CEA or CA 15-3 can precede clinical or radiologic evidence of recurrence by months and may help select patients for more sensitive imaging. Early after starting chemotherapy, transient paradoxical increases—most often in CA 15-3—can occur; repeating the measurement in 1–2 months is recommended before altering management. In advanced disease, periodic marker assessment interpreted with clinical and imaging data aids evaluation of therapeutic response, with greater sensitivity for distant metastases than for locoregional recurrence.