CA 27.29

This page was reviewed under our medical and editorial policy by

Bradford Tan, MD, Chair, Department of Pathology and Laboratory Medicine, City of Hope Atlanta, Chicago and Phoenix

This page was updated on June 7, 2023.

The cancer antigen 27.29 test (CA 27.29) is a blood test that measures the levels of glycoprotein produced by the mucin-1 (MUC1) gene.

The level of CA 27.29, also known as 27.29, is used as a tumor marker to measure the activity of the disease in patients with breast cancer. It’s one of several types of tumor markers used for breast cancer and is most commonly used in advanced breast cancer, as opposed to early-stage breast cancer.

Tumor markers, also known as biomarkers, measure proteins found in higher levels in patients with cancer, specifically in the:

  • Blood
  • Body tissues
  • Urine

To help answer common questions on CA 27.29, this guide will cover:

What is a CA 27.29 test used for?

The CA 27.29 test is used for measuring how cancer is progressing and how the body is responding to treatment.

A CA 27.29 blood test looks for a specific type of tumor marker produced by the MUC1 gene. Elevated levels of this type of cancer antigen may be found in patients with metastatic breast cancer, meaning breast cancer that’s spread to distant areas of the body. For this reason, clinical guidelines recommend that tumor markers are used for metastatic breast cancer only and not for screening, diagnosing or monitoring localized breast cancer.

Other types of cancers and noncancerous conditions may show elevated 27.29 levels, which is why tumor marker tests are often used in combination with other tests.

What is the difference between CA 15-3 and CA 27.29?

Another type of tumor marker, CA 15-3, also measures a similar antigen, but doctors generally choose one test or the other. They aren’t often used interchangeably for the same patient.

CA 27.29 levels and normal range

After a CA 27.29 test, doctors interpret the test results, which are measured in units per milliliter (U/mL). The normal range of CA 27.29 is 0 to 38 U/mL. If a patient’s CA 27.29 is elevated, this may indicate that further tests are needed.

However, every patient’s situation is unique, so it’s important for patients to speak to their doctor about specific CA 27.29 results and what they mean.

While CA 27.29 levels may be elevated due to metastatic breast cancer, they may also be raised by other health conditions, including:

  • Other cancer types
  • Localized breast cancer
  • Some noncancerous conditions

Ongoing cancer treatment may also impact CA 27.29 levels, since chemotherapy may increase levels in the body immediately after treatment. For this reason, doctors may wait to administer a CA 27.29 test until after the patient has finished a round of active treatment.

Understanding test results

While it’s normal for patients to feel anxious or worried when waiting for results, CA 27.29 fluctuations over time may occur, so test results are only one part of the bigger picture. Results may go up and down over time for different reasons, so careful interpretation is needed over the long term.

How accurate is CA 27.29?

While tumor markers like CA 27.29 have a strong association with metastatic breast cancer, these limitations are possible:

  • CA 27.29 levels may not increase until after the cancer has advanced.
  • Some patients with advanced cancers may not have increased levels, even though increased levels are likely.
  • Both false negatives and false positives may occur.
  • Increased CA 27.29 levels are most associated with metastatic breast cancer, but they may also be caused by other conditions, including ovarian cysts and cancerous and noncancerous conditions of the kidney, breast and liver.

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