What is the role of the CA27.29 (Cancer Antigen 27.29) test in monitoring a patient with a history of breast cancer?

CA27.29 Testing in Breast Cancer Monitoring

CA27.29 should NOT be used for routine surveillance after primary breast cancer treatment, as it does not improve survival, quality of life, or cost-effectiveness, and its only appropriate role is in monitoring response to therapy in patients with established metastatic disease. 1, 2, 3

When NOT to Use CA27.29

Screening, Diagnosis, and Staging

• Do not use CA27.29 for screening, diagnosis, or staging of breast cancer, as the data are insufficient to support these applications 1, 3
• The marker has poor sensitivity in early-stage disease, detecting only 33% of non-metastatic cases 4

Routine Surveillance After Primary Treatment

• Do not use CA27.29 for routine monitoring after completing primary breast cancer therapy, even if the marker was previously elevated 1, 2, 3
• While CA27.29 can predict recurrence 5-6 months before clinical symptoms, no prospective randomized trials demonstrate that earlier detection through marker monitoring improves disease-free survival, overall survival, or quality of life 1
• Normal CA27.29 levels do NOT rule out recurrence—the marker detects only 57.7% of recurrences, meaning 43% of recurrences occur with normal marker levels 2
• If markers normalize after primary treatment, discontinue routine monitoring and rely instead on clinical examination and symptom-directed imaging 2

When CA27.29 IS Appropriate

Monitoring Established Metastatic Disease

• Use CA27.29 only in patients with confirmed metastatic breast cancer during active therapy, always in combination with imaging and clinical assessment—never as a standalone test 3, 4
• CA27.29 is elevated in approximately 81% of metastatic cases 3
• A rising CA27.29 level ≥20% suggests treatment failure, particularly when measurable disease is absent on imaging 3
• A median increase of 32% indicates progressive disease, while a median decrease of 19% indicates stable or regressing disease 3

Interpretation Timing and Pitfalls

• Do not interpret CA27.29 levels during the first 4-6 weeks of new therapy, as spurious early rises can occur 3
• Always confirm elevated or rising CA27.29 with diagnostic imaging before modifying therapy 4
• Base treatment decisions on imaging and clinical assessment, not marker levels alone—a rising marker suggests treatment failure, but normal or stable markers do NOT confirm treatment success 2

Critical Clinical Pitfalls to Avoid

False Sense of Security

• Normal markers provide false reassurance given their poor sensitivity—up to 43% of recurrences occur with normal CA27.29 levels 2
• Many clinicians incorrectly order these tests for post-surgical follow-up, which leads to overdiagnosis without survival benefit 4

False Positive Elevations

• CA27.29 can be falsely elevated in benign conditions including pulmonary fibrosis, interstitial lung disease, liver disease, benign breast disease, and ovarian cysts 5, 6
• In patients with pulmonary fibrosis, CA27.29 may remain persistently elevated without evidence of malignancy and can normalize after lung transplantation 5

Marker Selection

• CA27.29 and CA15.3 provide comparable clinical utility and should not be used interchangeably in the same patient—choose one and maintain consistency 3, 7
• CA27.29 appears slightly more sensitive than CA15.3 across all breast cancer stages, particularly at low antigen concentrations 7

Algorithm for Clinical Decision-Making

For patients completing primary breast cancer treatment:

• Stop routine CA27.29 monitoring regardless of whether markers were previously elevated 2
• Use clinical examination and symptom-directed imaging for surveillance 2

For patients with suspected recurrence:

• Order imaging first, not CA27.29 2, 4
• If imaging is equivocal and CA27.29 is elevated, consider PET/CT (sensitivity 0.90, specificity 0.81, positive predictive value 0.97) 4

For patients with confirmed metastatic disease:

• Use CA27.29 alongside imaging to monitor treatment response 3
• Obtain baseline level before starting new therapy 3
• Wait 4-6 weeks after initiating therapy before interpreting changes 3
• A ≥20% rise suggests treatment failure; confirm with imaging before changing therapy 3