Multi-Cancer Early Detection Blood Tests: What They Are and Why They Are Still Being Studied

What the test is actually doing

Dying cancer cells shed material into the bloodstream: fragments of DNA, whole cells, proteins. A multi-cancer detection test, which NCI abbreviates MCD and companies often call MCED, takes a tube of blood and looks for that material.

NCI describes what current tests measure. Some look at changes in DNA or RNA sequence. Some look at patterns of DNA methylation, a chemical tag that changes how a gene is read. Some look at patterns of DNA fragmentation, meaning how the DNA has been broken up. Some measure protein markers, and some look for antibodies the body has made against growing cancer cells.

NCI notes that MCD and MCED refer to the same kind of test. It also states something these tests are often described as doing but do not: an MCD test makes a prediction about the presence of cancer, not a diagnosis.

Why it is different from other screening

Two things set it apart, and NCI names both.

First, it is one blood draw rather than an x-ray, a scan or a procedure like colonoscopy. Second, it checks for many cancer types at once, including some for which no screening test exists.

That second point is the real appeal. Pancreatic, ovarian and esophageal cancers have no population screening program, and they are diagnosed late. A test that could find them early would matter enormously. Our overview of cancer screening explains what a screening program has to prove first.

Where the evidence actually stands

This is the part the marketing tends to skip, and NCI is blunt about it.

No MCD test has been authorized by the FDA. Some companies offer them as laboratory developed tests, a category that lets a single laboratory design, make and run a test in-house.

No professional medical society and no US Preventive Services Task Force recommendation currently supports using MCD tests for cancer screening. Health insurance does not routinely cover them.

And the central sentence: to date, there are no definitive clinical trials showing that using MCD tests to screen people without symptoms will reduce overall cancer deaths.

NCI also reports a specific finding worth holding onto. In at least one study, half the people with a positive MCD test went through diagnostic testing and had no cancer found after a year of follow-up.

What a negative result does not mean

NCI states that people have been diagnosed with cancer despite a negative MCD test.

There are two ways that happens. The cancer may be a type the test does not look for. Or it may be a type the test does cover, at an early stage, and the test simply misses it.

Each test sets its own cut-point for calling a result positive or negative, based on a proprietary algorithm developed with machine learning. Those cut-points are not public and are not the same between tests.

NCI's answer to whether standard screening is still needed is one word: yes. A negative MCD result is not a reason to skip a mammogram, a Pap or HPV test, a colonoscopy or a lung CT. Our page on benefits and harms of screening covers why a test has to prove it lowers deaths, not just that it finds things.

The trial that will answer this

NCI's Cancer Screening Research Network has launched a pilot called the Vanguard Study.

It will enroll up to 24,000 people to work out whether a much larger randomized controlled trial is feasible. That larger trial would be the one to test whether the benefits of MCD screening outweigh the harms, and whether it finds cancer early in a way that actually reduces deaths.

Participants are randomized to a control arm or to one of two MCD arms. NCI selected two assays through a formal public process: the Avantect MCD Test from ClearNote Health and the Shield MCD Test from Guardant Health. They are not compared to each other, only to cancers found in the control arm. Control arm participants have blood drawn but no additional testing for now, and everyone in every arm is encouraged to keep up their usual screening.

When to get checked

An MCD test is not a substitute for noticing something. These changes warrant a doctor's appointment regardless of any blood test result:

• Unexplained weight loss of more than 5% of body weight over six to twelve months
• A cough, hoarseness or breathlessness lasting more than three weeks
• Blood in stool, urine, or coughed up, even once
• A new lump anywhere that is hard, fixed or growing
• Any vaginal bleeding after menopause
• Persistent difficulty swallowing, or new indigestion lasting more than three weeks
• Jaundice, meaning yellowing of the skin or the whites of the eyes

And keep the screening you are already eligible for. That is the part with proven mortality benefit.

What this does not mean

• MCD tests are not proven, but they are not disproven either. NCI's position is that the evidence does not yet exist, which is why the trials are running.
• A positive result is a prediction, not a diagnosis. NCI reports that in at least one study half of positive results led to no cancer found within a year.
• A negative result does not clear you. People have been diagnosed with cancer after one.
• The absence of FDA authorization does not mean these tests are unavailable. It means they are sold under a different regulatory route, without that review.
• Nothing here is advice for or against having a test. It is what the federal research agency currently says the evidence shows.

Sources

• NCI Division of Cancer Prevention, Questions and Answers about Multi-Cancer Detection Tests — https://prevention.cancer.gov/major-programs/cancer-screening-research-network-csrn/questions-and-answers-about-multi-cancer
• NCI Division of Cancer Prevention, Vanguard Study — https://prevention.cancer.gov/major-programs/cancer-screening-research-network-csrn/vanguard-study
• NCI Division of Cancer Prevention, Cancer Screening Research Network (CSRN) — https://prevention.cancer.gov/major-programs/cancer-screening-research-network-csrn
• NCI, Cancer Screening Tests — https://www.cancer.gov/about-cancer/screening/screening-tests
• SEER Cancer Stat Facts, Pancreatic Cancer — https://seer.cancer.gov/statfacts/html/pancreas.html

How this article was prepared

An AI-assisted editorial system helped prepare this page. No named medical reviewer has reviewed it unless one is listed.

The National Cancer Information Foundation publishes Cancer Explained. This page is for learning. It is not medical advice and does not suggest a test or treatment.

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