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, an elevated level does not always point to cancer—noncancerous conditions can sometimes cause a tumor marker level to increase.

Markers are also measured repeatedly 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 again and again to look at the trend over time, not just a single value. Because both cancer and noncancerous conditions can affect a marker, and because not everyone with a cancer has a raised marker, results are usually combined 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 is best understood in the context of your full picture.