Multi-cancer Early Detection (MCED) Tests

Multi-cancer early detection (MCED) tests are a new type of cancer screening that can look for signs of many types of cancer. These tests are still being studied and are not yet FDA-approved, but they hold promise for finding more cancers early. Understanding how they work and their current limits can help you make informed decisions about using one.

What are multi-cancer early detection tests?

Multi-cancer early detection (MCED) tests look for traces of more than one type of cancer, most often from a single blood sample. Some MCED tests may use urine, saliva, or other body fluids.

What do MCED tests look for?

MCED tests check blood samples for signs of cancer, such as pieces of DNA, RNA, or proteins from abnormal (cancer) cells. If the test finds something abnormal, it might mean that the person has cancer.

Some MCED tests may suggest where in the body the cancer started. Others may only show that cancer could be present, without identifying the type or location.

Do MCED tests diagnose cancer?

No. MCED tests do not diagnose cancer. If a result is positive, more tests will be needed to confirm whether cancer is present, what type it is, and where it’s located.

Like all medical tests, MCED test results can sometimes be wrong. (See “What do we still need to know about MCED tests?” below.)

Why are MCED tests being developed?

Many companies are developing MCED tests to find cancers earlier—ideally, before symptoms appear. Finding cancer early increases the chances it can be treated successfully.

Currently, proven screening (early detection) tests exist for only a few cancers (including breast, cervical, colorectal, prostate, and lung). Getting these tests as recommended has been shown to help find and treat these cancers earlier than waiting for symptoms.

But most cancers don’t have proven screening tests. In fact, nearly half of all cancers diagnosed each year are cancers with no recommended screening tests. These cancers are often found at later stages, when they can be harder to treat.

MCED tests might be able to find a wide range of cancers earlier, hopefully before a person has any symptoms.

Are MCED tests FDA approved?

No. MCED tests have not been FDA cleared or approved yet. However, some are offered as lab-developed tests under the Clinical Laboratory Improvement Act (CLIA) regulations, which allows doctors to order them.

More research is needed before these MCED tests can be recommended for widespread use in people with no symptoms of cancer. Many companies are studying these tests and gathering data to seek FDA approval.

Most test makers say that MCED tests are not meant to replace current screening tests (such as mammograms for breast cancer, Pap tests and HPV tests for cervical cancer, stool tests and colonoscopy for colorectal cancer, the PSA blood test for prostate cancer, and low-dose CT scans for lung cancer). Instead, MCED tests might one day supplement current screening tests, and also help find cancers we don’t yet have proven screening tests for.

The GRAIL Galleri test

The GRAIL Galleri test is a blood-based MCED test that became available in 2024. Here’s what to know:

• It’s not FDA approved, but it is available under CLIA because the testing is done in a central lab. This means doctors can order the test.
• It costs many hundreds of dollars. Many people will have to pay out of pocket. Most insurance plans don’t cover it, though some employers might help with some or all of the cost. Additional testing after a positive test result can also be costly.
• It doesn’t find all cancers. Ongoing studies will help show how accurate it is for different types of cancer.
• Results can be unclear. The test might suggest something is wrong when there’s no cancer (a false positive), or it might miss a cancer that’s present (a false negative). It’s also possible that the test might find a cancer, but the cancer’s exact location can’t be found.

What do we still need to know about MCED tests?

Here are some of the questions about MCED tests (including the Galleri test) that still need to be answered. 

• How accurate are MCED tests? There is much that still needs to be learned about the accuracy of these tests for all cancers and for individual cancer types. A test that checks for many cancers may detect some types of cancer better than others.
• Who should be tested? It’s not yet clear whether MCED tests will be best used for general cancer screening, or for specific groups, such as people at higher cancer risk because of age, sex, family history, exposures, or other factors. A person’s life expectancy or their willingness and ability to follow up on test results might also matter.
• How early can an MCED detect a cancer? A successful MCED test would find cancer early enough to improve treatment outcomes when compared to cancers found after symptoms have started.
• Do they save lives? It is not known whether MCED testing reduces the number of deaths caused by cancer. Researchers still need to learn whether earlier detection with MCEDs and treating the cancer earlier improves outcomes, including the risk of dying from cancer.
• What should happen after a positive MCED test result? Doctors need clear guidance on what tests should be done after a positive MCED test—and how to proceed if those tests don’t find cancer.
• How often should the test be done? The ideal amount of time between MCED tests still needs to be determined. Different cancers can grow at different rates. Waiting too long between tests might miss some cancers, but having a test too often (when it isn't needed) could be a waste of important medical resources.

Along with needing to know more about the best ways to use MCEDs, there is the chance of having possible inaccurate or unclear test results.

• What about false-positive results? So far, research has shown that about half of people with positive MCED tests are found not to have cancer when further testing is done. False-positive test results can cause anxiety and lead to unnecessary tests.  
• What about false-negative results? A false-negative result might give a false sense of security and could delay a cancer diagnosis. Although a negative MCED test result usually means a person has a very low risk for having cancer at that time, it’s important not to ignore new symptoms and signs that could be from cancer, and to continue with recommended screening tests.

Expert guidance for shared decision-making with MCED testing

At this time, there are no clinical practice guidelines or official recommendations for using MCEDs in the United States.

Because of the potential importance of these tests, cancer screening experts have developed MCED guidance for primary care (family) doctors and their health care teams to help guide discussions with patients. The key points for discussion are not recommendations for using MCED tests, but they are designed to encourage shared decision-making between people and their doctors when considering screening with one of these tests.

The importance of shared decision-making

Because there are so many uncertainties about MCED tests, it’s important that you talk with your doctor about whether testing right for you. This is called shared decision-making.Shared decision-making means you are getting enough information about MCEDs to make an informed decision about whether or not to use them.

MCED testing conversations should include information about the potential benefits, limits, harms, and uncertainties around MCED testing.

It’s also important to consider your personal values and preferences. For example, if a person isn’t willing to get more testing if they have a positive MCED test result, they may not be a good candidate for MCED testing.

It’s important to remember that MCED tests should not replace recommended screenings for breast, cervical, colorectal, lung, and prostate cancers.

Questions to ask your doctor or health care team about MCED testing

If you are considering having an MCED test, here are some key questions to ask. This can help guide the conversation with your doctor and health care team.

• What is an MCED test?
• What MCED tests are available?
• Would I be a good candidate for MCED testing?
• How much does the test cost? Will insurance cover it?
• What are the possible benefits of MCED testing?
• What are the possible limits, harms, and uncertainties of MCED testing?
• How often would I need to get the test?

What work is the American Cancer Society (ACS) doing related to MCEDs?

The American Cancer Society is addressing the promise and use of MCED tests on several fronts.

ACS research on MCED testing

ACS funds and conducts research to support advancing the potential use of MCED tests. ACS believes that if these tests are successful, they could save many lives that would otherwise be lost. ACS researchers have also worked with developers of some of these tests to provide guidance and, in some instances, to allow them to measure the accuracy of their tests within our population studies (through research collaborations).

Advocacy for access to MCED tests

The American Cancer Society Cancer Action Network (ACS CAN) works to pass laws and regulations across the country that could benefit people with cancer or who might have cancer. One effort is working to pass the Nancy Gardner Sewell Medicare Multi-Cancer Early Detection (MCED) Screening Coverage Act. This act would create a pathway for older adults and others on Medicare to get these tests once they are approved by the FDA and shown to have clinical benefit.