Tumor markers (like PSA, CA 125, CA 15-3, and CA 19-9) aren’t as reliable as most people think, and they can sometimes fluctuate widely for no apparent reason. Used inappropriately (either too often or for the wrong types of cancer situation) and tumor markers can create a lot of confusion, unnecessary testing, and unhelpful stress – while not improving your odds.

They can be useful periodically during treatment to assess how well treatment is working (though it usually requires other tests besides a tumor marker to be sure). And tumor markers are sometimes useful in prostate and ovarian cancer during surveillance (when treatment is complete, and people are monitored for possible relapse).