Tumor Marker for Breast Cancer
The Ca 27-29 blood test has a "normal" level below 30. Is it possible for the level to reach zero in a person who had invasive cancer with no lymph node involvement?
Suzanne M. McGettigan, MSN, CRNP, AOCN, Board Certified Adult Nurse Practitioner and a Certified Oncology Advanced Practice Nurse, responds:
A tumor marker is a substance that is produced by the body in response to cancer, or is produced by the cancer itself. Some of these markers are specific to one cancer, while others are seen in several types of cancer. These markers are generally used to evaluate the patient's response to treatment or to monitor for recurrence (return of the cancer after treatment). There are non-cancerous conditions that can cause markers to be elevated, so these must also be considered when interpreting the test results. Tumor markers can be used in conjunction with other tests (scans, biopsies, etc.) to help diagnose a patient who has symptoms suspicious for cancer. Some markers can help physicians to determine prognosis and treatment.
The CA 27-29 is a tumor marker that is most often used in people with breast cancer. In general, the number is not elevated in people with early stage cancers. If someone had an isolated recurrence that resulted in an elevated level and the tumor was surgically removed, the CA 27-29 could go to zero, or within normal range, after surgery.
In metastatic cancer, the CA 27-29 level does not ever go down to zero, but it can dip back into the normal range. More than the actual number, we follow trends of the marker to see if it is going up or down, or remaining stable. The result may be used in conjunction with radiology studies if recurrence or progression is suspected.
This test is far from perfect, as some women with metastatic disease never have an elevation in the tumor markers. Benign conditions, such as ovarian cysts, fibroids, liver and kidney disorders, and benign breast problems can result in elevated CA 27-29 levels. It can take 1-3 months after starting a new treatment for results to begin to decrease, so we typically wait 2-3 months to recheck CA 27-29.