Dear Dr. Roach: Would you please discuss the meaning and significance of blood tests to show the level of cancer markers to identify cancer and track the efficacy of treatments? I am 69 years old and have metastatic breast cancer, diagnosed in July 2022. The primary cancer was treated in 2018-2019 with surgery, chemotherapy and radiation. All during the treatment, my oncologist ordered bloodwork to monitor the level of CA-15-3 and CA 27.29. At the end of treatment, when a PET-CT scan showed no traces of cancer, the levels of the markers were in the low 20s.
During my three years of remission, my oncologist never checked the levels of the markers, stating that they weren’t diagnostic tools, but rather were used only to show trends during treatment. In July 2022, I had a breathing crisis, and CT scans showed a new mass. At that point, the markers were in the 130 range. I started treatment, and regular bloodwork showed those markers decreasing until February 2023. I’m now receiving new treatment to keep the tumor down. The last lab report showed that the cancer markers have decreased somewhat, so it looks like this therapy is working.
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Could the markers have been checked regularly during my remission to identify a recurrence prior to the breathing crisis I experienced in July 2022? Are there other cancers that can be detected through labwork to identify potential cancer developing? — A.A.
Answer: I am sorry to hear your cancer came back. There are a host of new treatments for metastatic breast cancer, much better than what we have had in the past.
Tumor markers, like CA-15-3 and CA 27.29, are blood tests that tend to correlate with specific cancer activity. Prostate specific antigen, or PSA, in prostate cancer is one of the most commonly known, and it’s one of the few found useful for screening. A healthy person should have very low amounts of the tumor marker, while a person with extensive cancer should have a very high level. However, no tumor marker is perfect — they can be elevated when there is no cancer, and low even when there is extensive disease. In people who had a high level when the cancer was first diagnosed, a trend of increasing blood levels (not just a single reading, which could be misleadingly false) strongly suggests cancer recurrence. These markers are most useful in people with breast cancer that is known to have spread to distant sites, such as lung or bones.
While some breast oncologists will order tumor markers or imaging studies like CT scans in people who are thought to be in remission, the recommendation is not to check these in people who’ve had breast cancer but are feeling fine. Studies to see whether they help have shown no benefit. There is the potential for harm from unnecessary evaluation for false positive results. The current recommendation is for mammograms (unless a person has had a mastectomy) and a careful physical exam and history.
New technology called “cell-free DNA” (sometimes called “liquid biopsy”) may have the potential to revolutionize both surveillance after treatment as well as early detection of cancer. Clinical trials are in process. I suspect we will learn many new lessons about cancer development, similar to the lessons we learned when highly detailed imaging studies like MRI became available. Hopefully, this new screening and detection tool will lead to improved treatment and cures for early cancers.
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