About 264,000 American women are diagnosed with breast cancer each year—a staggering statistic. If you’re one of them, you’re likely all too familiar with the poking and prodding that’s part of breast cancer treatment, as your medical team frequently needs to check your blood. They do this to keep tabs on a few things, one of which is your tumor markers. These markers can give your doctors hints about how active your cancer is and if it’s responding to the treatment protocol. “That said, they’re not great tests,” says Jules Cohen, M.D., a medical oncologist and clinical assistant professor of medicine at Stony Brook University in Stony Brook, NY. “They have some limitations.” Here’s what you need to know about tumor markers for breast cancer—and what they can (and can’t) tell you about your disease.
Why Are Tumor Marker Tests Used for Breast Cancer?
There are two main types of tumor markers: circulating tumor markers and tumor tissue markers (these are also known as cell markers).
Circulating tumor markers are proteins or other substances pumped out by cancer cells that wind up in your bloodstream, stool, and urine when you have certain cancers. The levels in your blood can give your doctor an idea about how active your cancer is, your prognosis, if your cancer has returned, and how it’s responding to treatment. “Elevated tumor markers are typically associated with a higher burden of disease,” says Dr. Cohen. Your doctor may check them regularly during your course of treatment to see how the markers are changing over time, as well as after treatment to monitor for recurrence.
Then there are tumor tissue or cell markers—sometimes referred to as biomarkers—which are found in the tissue of the tumor itself. They’re used more when determining the type of breast cancer you have: human epidermal growth factor receptor 2 (HER2+), estrogen (ER+) or progesterone receptor positive (PR+). “These tumor markers tell us about the specific biology of the cancer,” says Amber Guth, M.D., professor of surgery and director of breast cancer interdisciplinary fellowship at NYU Langone Health in New York City. They can also help determine your prognosis as we know some cancers are more aggressive than others, and they can help doctors put together individualized treatment. For example, for HER2+ breast cancer, there are targeted treatments that address this specific genetic mutation.
“Tumor markers are not useful in early-stage breast cancer,” says Dr. Cohen. “Generally, they’re more useful when you have metastatic disease, when your cancer has spread beyond the breast and the local regional lymph nodes to other areas of the body such as the liver, lungs, or bone,” he says. For example, research has shown that the tumor marker CA 15-3 (more on it below) is elevated in less than 50% of those with early-stage localized breast cancer, but it’s high in 80% of those with metastatic disease. As metastatic patients are treated with either hormonal therapy, targeted treatments, or chemotherapy, the tumor markers will start to decrease, he says. “If the cancer becomes resistant to one of these systemic therapies, one of the early signs of that resistance will be rising tumor markers.
What Are the Tumor Markers for Breast Cancer?
Not all cancers have known tumor markers, but breast cancer does have a few specific markers that doctors will check for. These include:
Cancer-antigen (CA) 15-3: This tumor marker is specific to breast cancer.
CA 27.29: This marker is interchangeable with CA 15-3, so doctors will generally check one or the other.
Carcinoembryonic antigen (CEA): This tumor marker is elevated in breast cancer patients, as well as colon, stomach, and lung cancer patients.
CA-125: This one is associated with ovarian cancer and ascites, which is when fluid made up of malignant cells collects in the stomach. In some cases, CA-125 is elevated with metastatic breast cancer.
Circulating tumor cells (CTCs): These are cells that break off from the cancer and find their way into your bloodstream. If your CTCs level is elevated, it’s an indication that your cancer may be growing.
What to Expect With Your Tumor Marker Test
Circulating tumor markers are obtained during a simple blood or urine test—and there’s no special prep or downtime. If you’re getting a blood test, your provider will collect blood via needle in a vial that will then be sent to a lab to be analyzed. If you’re having a urine test, you’ll need to urinate into a sterile container, which will also then be sent to a lab. Thankfully, circulating tumor marker numbers come back quickly, so your doctor should have the results within a day or two. (If you haven’t heard from your doctor’s office by then, you can call to check in).
If you’re having tissue biomarkers tested, your doctor will use a special needle to get a sample of tissue in the tumor and send it out for a biopsy. Then, you wait. Tissue biopsies take a bit longer—as long as two to four weeks.
What Do Your Results Mean?
Your circulating tumor marker blood test results will include a numerical value that will either be in a normal range or considered high. Below are the ranges for the tumor markers above, according to the National Institute of Cancer.
CA 15-3: Normal, less than 30U/mL. High, 30 U/mL or higher.
CA 27-29: Normal, less than 38 U/mL. High, 38 U/mL or higher.
CEA: Normal, less than 2.5 ng/mL. Extensive disease, greater than 10 ng/mL. Metastatic disease, greater than 20 ng/mL.
CA 125: Normal, less than 35 U/mL. High, greater than 35 U/mL.
CTCs: Normal, n/a. High, greater than 5 CTCs per 7.5 mL of blood.
As mentioned, when the markers are in that high threshold, that could indicate more active disease. However, it’s not a perfect science. You may experience fluctuations even when your cancer hasn’t spread. “What we really look at are the trends over time—if the tumor marker is consistently going up month after month,” says Dr. Cohen. When that happens, it means your cancer is possibly resistant to the treatment and your doctor will likely order more tests, including another set of scans (PET, CT, MRI, etc.) to confirm. “We seldom make decisions based on the tumor markers alone,” he says.
Limitations of Tumor Marker Blood Tests
While these tests are certainly helpful, they are not without their drawbacks. For instance, according to Dr. Guth, the breast cancer tumor markers are not as specific as the one used for prostate cancer, prostate specific antigen (PSA), and they can be falsely elevated. Factors such as smoking and certain medications can cause them to go up, too, she says.
Some patients become fixated on the numbers, which isn’t ideal, given that they are just one piece of the puzzle. “They develop an obsession with their tumor markers, and we try to caution against that because, in my eyes, they’re the least important parameter we follow,” says Dr. Cohen. What’s more important in a metastatic patient is how they are feeling, how symptomatic they are, and, of course, what the scans show.
Tumor markers can be an important tool in tracking your breast cancer treatment and disease progression, but on their own, the numbers are inconclusive. They may, however, prompt your doctors to order more tests, including radiology imaging, to get a full picture of your breast cancer.