[Edit: markers updated 4/26/19]

Tumor markers are basically substances that are found at higher than normal levels in the blood of some people with cancer. A cancer tumor often produces a specific protein in the blood that serves as a marker for the cancer. There are three tumor markers that are commonly used in metastatic breast cancer: cancer antigen 15-3 (CA 15-3), cancer antigen 27.29 (CA 27.29), and carcinoembryonic antigen (CEA). Oncologists sometimes monitor these markers to help determine how well you are responding to a particular treatment.

To be more specific on what they measure, this is one of the best definitions I’ve found for CA 27.29:

“CA 27.29 is an antigen—that is, a specific type of protein present on the surface of cells and is produced by a gene called MUC-1. CA-27 is a “glycoproteins,” (glyco means sugar) and may be present on the surface of epithelial cells like breast cancer cells. Breast cancer cells can shed copies of the CA 27.29 protein into the bloodstream too.” (reference)

For CA 15-3, it’s a protein that your breast tissue normally produces. However, if there is a cancerous tumor in your breast, the levels may increase as the number of cancer cells increase.

One thing I learned early on is that tumor markers are not very reliable and very greatly in their reliability from person to person. They can be the source of great anxiety but it’s really important to just keep them in perspective. They are just one tool that your oncologist will use in conjunction with your scans and other tests. I currently get my markers done every month. I’ve heard of some oncologists who don’t even use them because they can be unreliable.

To give an example, here are the most recent graphs of my tumor markers:

It’s a little blurry, but this is my Carcinoembryonic Antigen (CEA). You can just imagine how I felt when I saw the first reading after I started my treatment in early May, 2017. It leapt up! My oncologist said it was pretty common to have your markers jump after you first start treatment. It’s all the dead cancer cells now circulating in your blood. It swung down for a while and when it start climbing again in March, 2018, it made me a little nervous. Here’s another test:

This is my Cancer Antigen 27.29. Aside from the initial spike, it’s been on a downward slope. And lastly:

This is my Cancer Antigen 15-3 chart. This has also been trending downward after the initial spike.

So what do these mean? Not much on their own. They are simply data points to use in combination with other things like scans (PET/CT), blood tests (Comprehensive Metabolic Panel), biopsies and physical exams. During all of this time, I’ve felt great. My PET/CT scans have all been “stable” with a little regression on a few of them. So, even though my tumor markers have been jumping around a bit, I don’t really fuss too much about them alone. They need to be taken in context with other tests.

My advice would be to be glad to have the information, but don’t allow yourself to freak out over a rising number here or there. Look at it holistically in conjunction with everything else.