Why do tumor marker levels go up and down?

Tumor marker levels can change for more than one reason, and a change does not have a single meaning on its own. According to the National Cancer Institute, a high level does not always point to cancer. Conditions that are not cancer can sometimes raise a tumor marker level.

Markers are also measured again and again on purpose. The NCI explains that periodic, or "serial," measurements taken while someone is undergoing treatment can indicate whether the tumor is responding to treatment. After treatment ends, measuring tumor markers from time to time may be used to check whether cancer has returned.

So a level may be checked over and over to follow the trend, not just to read one value. Cancer and other conditions can both affect a marker. And not everyone with a cancer has a raised marker. That is why results are usually paired with other tests, such as biopsies or imaging.

Your health care team can explain what your own results mean, including any change from one test to the next. A single number makes the most sense in the context of your full picture.