Can tumor markers be used to screen for cancer?
Mostly, no. Researchers once hoped that markers measured in blood or other fluids could find cancer early, before symptoms. The National Cancer Institute reports that studies have generally found circulating tumor markers do not work well for screening.
A tumor marker, in NCI's definition, is anything present in or produced by cancer cells, or by other cells responding to cancer or to certain benign conditions, that provides information about a cancer. Traditionally these are proteins made in larger amounts by cancer cells than by normal ones, found in blood, urine, stool, tumors, or other tissues and fluids.
Two ways a screening test fails
NCI names both failures plainly. Markers often do not identify everyone with the disease, meaning they are not sensitive enough. Or they suggest cancer in people who do not have it, meaning they are not specific enough.
Each failure costs something different. A test that misses cancer gives false reassurance, and someone with real symptoms may wait months before pushing further. A test that flags healthy people sends them into scans, biopsies, and months of fear for nothing.
The second problem is worse than instinct suggests. Notice that NCI's own definition allows benign conditions to raise a marker. Meanwhile a small early cancer may shed too little to register at all. So the signal is weakest exactly when it would be most useful.
The exception, and how carefully it is handled
One marker is used in screening: prostate-specific antigen, or PSA. The way it is treated shows how much caution these tests require.
The U.S. Preventive Services Task Force does not simply endorse it. For men aged 55 to 69 it calls the decision an individual one, a grade C recommendation, and says clinicians should not screen men who do not express a preference for it. For men 70 and older it recommends against PSA-based screening, a grade D.
The numbers explain that caution. USPSTF says screening in men aged 55 to 69 may prevent about 1.3 prostate cancer deaths per 1,000 men screened over roughly 13 years, and about 3 cases of metastatic disease. It also notes that screening trials have shown no reduction in all-cause mortality.
Against that sit the harms. In Sweden, where a low PSA threshold of 3.0 ng/mL was used and men were screened every 2 years, more than 45% of men who took part in all screening rounds had a false-positive result over 10 years. Follow-up of large randomized trials suggests 20% to 50% of prostate cancers found by screening may be overdiagnosed, meaning they would never have caused symptoms in that person's lifetime.
One caveat about that source. The USPSTF statement is dated May 8, 2018, and the Task Force's own page says the topic is being updated.
Where markers genuinely earn their place
Once cancer is known to be present, markers become useful. NCI describes repeated measurements during treatment to see whether the tumor is responding, and measurements afterward to check for recurrence. Genomic markers found in tumor tissue can help match a treatment to a specific cancer.
The difference is the starting point. Watching a number move in someone with a known diagnosis is a very different task from finding disease in a healthy crowd. Our guide to tumor markers covers how they are read, and can tumor markers be normal when someone has cancer covers the sensitivity problem in practice.
The new blood tests, and what is not yet known
Multi-cancer detection tests, or MCDs, analyze many biomarkers at once in the blood of people without symptoms. Most examine DNA that tumor cells release into blood, and some also look at proteins. These are sometimes called liquid biopsy tests.
NCI's position is careful. Many are in development and several are already being marketed, but much remains to be learned about how best to use them and about their harms and benefits. The critical question it names is whether treating the cancers these tests find would actually reduce deaths from them. NCI says it will be launching a clinical trial to find out.
Until then, the practical advice is to use the screening tests shown to work for a given age and history, and to treat a mildly abnormal marker as a question rather than an answer.
Sources
Want the full picture? Read our complete explanation: Tumor Markers: What They Mean in Cancer Care
Know someone who needs this?
Plenty of people are looking for something like this and do not know where to start. If this would help a friend or someone you love, send it on — we have written an opening line so you do not have to stare at an empty message. You can change every word of it.
Your message is written and sent in your own email or messaging app — we never see who you send it to, and nothing is added to any list.