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Blood Test Tracker

CA 27.29

A protein from the same family as CA 15-3. Doctors use it to follow breast cancer treatment and recurrence, and harmless conditions can raise it too.

AI-verified against cited sources. Awaiting expert reviewAlso called CA 27.29, CA27.29, BR 27.29LOINC 17842-6

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What it is

CA 27.29 measures a form of a protein called MUC1, which sits on the surface of breast and other gland cells. Small amounts are normally in the blood. Breast cancer cells that have spread can release more of it. Some harmless conditions raise it as well. It is closely related to CA 15-3, but the two tests give different numbers.

Why it matters

CA 27.29 is used in people who already have breast cancer. Mayo Clinic Laboratories lists these uses: following people with spread (metastatic) disease, and serial testing in women treated for stage II or III breast cancer who have no signs of disease. It is not useful for finding breast cancer in people who haven't been diagnosed. ASCO (2013) does not recommend tumor marker tests, including CA 27.29, for routine follow-up after treatment aimed at cure in people with no symptoms and a normal exam.

If it’s high

A result above your lab's range does not mean you have cancer or that cancer has come back. Liver conditions, benign breast disease, lung conditions and some autoimmune diseases can raise CA 27.29. In a person who is being followed after breast cancer, clinicians watch the trend over several tests, along with imaging and symptoms.

Common causes

  • Long-term liver disease, such as chronic hepatitis or cirrhosis
  • Benign (non-cancer) breast disease
  • Autoimmune conditions such as lupus
  • Lung conditions such as tuberculosis, sarcoidosis or interstitial lung disease
  • Breast cancer, especially when it has spread
  • Other cancers, such as lung, colon, pancreas, liver, ovary, cervix or uterus

What can help

  • Ask your clinician whether to repeat the test, and compare it with earlier results from the same lab
  • Tell your clinician about liver, lung or autoimmune conditions and about recent infections
  • Ask how this result fits with your scans and exams
  • Use the same lab and method for follow-up tests

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 0–38.6 U/mL. Source: Labcorp, Mayo Clinic Laboratories (Extended Catalog).

What can affect your result

  • Assay method: results differ between labs and can't be compared directly
  • Liver disease and several other non-cancer conditions
  • Stage of disease: this test is aimed at people who have already had breast cancer
  • Liver disease, benign breast disease, lung conditions, some autoimmune and infectious diseases and other non-cancer conditions can raise CA 27.29 (the same MUC1 family as CA 15-3).
  • Results from different methods can't be compared directly, so use the same lab and method when following results over time (Labcorp, Mayo).
  • CA 27.29 and CA 15-3 are related but not interchangeable tests.
  • Quest rejects grossly hemolyzed samples.

When to talk to a clinician

Talk with your clinician soon if you are being followed for breast cancer and your CA 27.29 is rising on repeat tests, or if you notice a new breast lump or skin change, bone pain that doesn't go away, new shortness of breath, or unexplained weight loss. If you have never had breast cancer and this test was ordered for another reason, a result above range is worth discussing, but it is most often explained by something harmless.

Questions you could ask

  • Why was CA 27.29 ordered for me, and how will we use the result?
  • Should I use the same lab each time so the results can be compared?
  • Could a liver, lung, autoimmune or other non-cancer condition explain this number?
  • Should we repeat it, and compare it with my earlier results?
  • How does this result fit with my scans and exams?

Questions people ask

Is CA 27.29 a test for finding breast cancer?

No. It is used in people who have already been diagnosed and treated, as one tool along with exams and imaging. Harmless conditions can raise it, and it is rarely raised in early disease. Your care team decides whether it's useful in your case.

Is CA 27.29 the same as CA 15-3?

No. They measure related proteins from the same gene, and doctors use them in much the same way, but the numbers aren't interchangeable. Use the same test and the same lab if you are following your results over time.

Show the science and sources

Units

  • 1 U/mL = 1 U/mL
  • 1 U/mL = 1 kU/L

For clinicians and researchers

CA 27.29 (BR 27.29) is a highly polymorphic glycoprotein of the MUC1 family, a product of the MUC1 gene (Labcorp). CA 15-3 and CA 27.29 assays measure slightly different parts of the MUC1 tandem-repeat molecule. In College of American Pathologists survey data from 10 methods covering both analytes, regression slopes between methods ranged from 0.836 to 1.095, mostly because of differences in calibration (Klee and Schreiber 2004). Mayo (chemiluminometric immunoassay) lists its uses as monitoring progression or regression in metastatic disease, serial testing in women with prior stage II or III disease who are clinically free of disease, and possibly predicting early recurrence; it is not useful for screening or diagnosis. Labcorp (immunochemiluminometric assay) limits use to patients previously treated for stage II or III breast cancer, together with other clinical methods. The NCI lists CA 27.29 for detecting metastasis or recurrence. ASCO 2013 does not recommend CEA, CA 15-3 or CA 27.29 for routine follow-up of asymptomatic patients with a normal exam, and NACB 2008 says CA 15-3 or BR 27.29 may be used for therapy monitoring in advanced disease. Non-malignant causes of raised CA 15-3 and CA 27.29 include chronic hepatitis, cirrhosis, tuberculosis, lupus, sarcoidosis and interstitial lung disease (2024 case report discussion). Reference limits: Labcorp 0 to 38.6 U/mL; Mayo 38.0 U/mL or lower for adults 18 and older, with use in men not defined. Both note that serum markers aren't specific for malignancy and that values may vary by method.

LOINC 17842-6 (primary). Specimen: serum.

Sources

  1. Cancer Antigen (CA) 27.29 (test 140293), Labcorp
  2. C2729 - Breast Carcinoma-Associated Antigen, Serum, Mayo Clinic Laboratories (Extended Catalog)
  3. CA 27.29 (test code 29493), Quest Diagnostics
  4. Breast cancer follow-up and management after primary treatment: American Society of Clinical Oncology clinical practice guideline update, Journal of Clinical Oncology (2013)
  5. MUC1 gene-derived glycoprotein assays for monitoring breast cancer (CA 15-3, CA 27.29, BR): are they measuring the same antigen?, Archives of Pathology & Laboratory Medicine (2004)
  6. Hypermetabolic Pulmonary and Mediastinal Lesions With Elevated Cancer Antigen (CA) 15-3 and CA 27-29 in a Patient With a History of Ovarian and Breast Cancer, Cureus (2024)
  7. National Academy of Clinical Biochemistry laboratory medicine practice guidelines for use of tumor markers in testicular, prostate, colorectal, breast, and ovarian cancers, Clinical Chemistry (2008)
  8. Tumor Marker Tests in Common Use, National Cancer Institute (2023)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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