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A blood test for cancer is now available, but is it ready for prime time?

A new blood test that can detect up to 50 cancers from a single blood sample is gaining traction in the United States.

The Galleri blood test is being offered by several U.S. health networks, which have teamed up with the company that developed it. They include the Department of Veterans Affairs, Mercy Health, Ochsner Health, Intermountain Healthcare, Community Health Network, Knight Cancer Institute at Oregon Health & Science University, Premier, and Cleveland Clinic.

Cleveland Clinic’s Eric Klein, MD, is enthusiastic about the test, describing it in a blog post as “game-changing” because it can detect many different cancers and at a very early stage. Current screening for cancer focuses on one cancer at a time: for example, mammograms for breast cancer and colonoscopy for colorectal cancer.

In contrast, the Galleri test involves just one blood sample, which is then analyzed for particles that are shed by all cancers into the bloodstream, known as cell-free or circulating tumor DNA. It detects whether there is cancer present, and where cancer may be.

This test “completely changes the way we think about screening for cancer,” says Jeff Venstrom, MD, chief medical officer at GRAIL, the company marketing the test. But there is some concern among doctors that widespread use of the test is premature.

Having a blood test for multiple cancers is a “very good idea, and the scientific basis for this platform is sound,” says Timothy Rebbeck, Ph.D., with the Harvard T.H. Chan School of Public Health and the Dana-Farber Cancer Institute in Boston. “But the devil is in the details to ensure the test can accurately detect very early cancers and there is a pathway for subsequent workup (diagnosis, monitoring, treatment, etc.),” he says.

Galleri is being offered to people who are older than 50 and who have a family history of cancer, who are at higher risk for cancer, or who have compromised immune systems. The company recommends that people interested in the test get in touch with their health care provider, who then needs to register with GRAIL and order the test.

In addition to a prescription from a health care provider, people who want the test will have to pay for it out of pocket, around $950. The test is not covered by medical insurance, and the FDA has not approved it.

The company emphasizes that the Galleri test is intended to complement (not replace) recommended cancer screenings, such as mammograms.

This is a “screening” test for people who do not have cancer, and so it is intended to be used by primary care doctors, Rebbeck says. He warns that “clinical pathways are not yet in place” for primary care providers to process the results of the test, although he says they are being developed.

The test returns one of two possible results – either “positive, cancer signal detected” or “negative, no cancer signal detected.”

According to the company, the test also predicts where the cancer sign is coming from “with high accuracy,” which helps guide the next steps to diagnosis.

One problem is a patient may face multiple follow-up tests if their test comes back positive, says Sameek Roychowdhury, MD, Ph.D., with the Ohio State University Comprehensive Cancer Center in Columbus.

“Not everybody will have actual cancer, but they may undergo many tests, with a lot of stress and cost, and still not find anything. I can tell you every time someone undergoes a test looking for cancer, that is not an easy day,” he says.

In a large-scale study, the Galleri test had a “false-positive” rate of less than 1%. This means that in roughly 200 people tested without cancer, only one received a result saying cancer was detected when it wasn’t there. The accuracy of the test varies with different types of cancers, and also how advanced they are.

Rebbeck says the test is still “relatively poor for detecting very early cancers, so it will need additional tweaking before it achieves the goal of multi-cancer early detection.”

Venstrom acknowledges that the test is “not perfect yet” and says the company will continue to update and improve its performance. New data is expected in September, he says.

Data on how the test performs in clinical practice is being gathered in the United Kingdom, where the Galleri test is being used in a large trial by the National Health Service (NHS). About 140,000 healthy cancer-free volunteers have signed on to take part in the trial.

A blood test for cancer is now available, but is it ready for prime time?

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