Blood Test for Cancer Available, but Is It Ready for Prime Time?

Megan Brooks

August 08, 2022

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

The Galleri blood test is being now offered by a number of US health networks.

The company marketing the test, GRAIL, has established partnerships with the US 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, among others.

Cleveland Clinic's Eric Klein, MD, emeritus chair of the Glickman Urological Kidney Institute, is enthusiastic about the test, describing it as a "game-changer" and emphasizing that it can detect many different cancers and at a very early stage.

"It completely changes the way we think about screening for cancer," commented Jeff Venstrom, MD, chief medical officer at GRAIL. He joined the company because "there are not many things in life where you can be part of a disruptive paradigm and disruptive technology, and this really is disruptive," he said in an interview.

"The Devil Is In the Details"

But there is some concern among clinicians that widespread clinical use of the test may be premature.

Having a blood test for multiple cancers is a "very good idea and the scientific basis for this platform is sound," commented Timothy R. Rebbeck, PhD, professor of cancer prevention, Harvard T.H. Chan School of Public Health, and Division of Population Sciences, Dana-Farber Cancer Institute, 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)," Rebbeck told Medscape Medical News..

Galleri is offering the test to individuals who are older than 50 and have a family history of cancer, or those who are high risk for cancer or immunocompromised. They suggest that interested individuals get in touch with their healthcare professional, who then needs to register with GRAIL and order the test.

As well as needing a prescription, interested individuals will have to pay for it out of pocket, around $950. The test is not covered by medical insurance and is not approved by the US Food and Drug Administration.

Falls Into Primary Care Setting

Rebbeck commented that Galleri is a screening test for individuals who don't have cancer, and so the test is intended to fall into the primary care setting. But he warned that "clinical pathways are not yet in place (but are being developed) so that primary care providers can effectively use them." Rebbeck cautioned.

The test uses next-generation sequencing to analyze the arrangement of methyl groups on circulating tumor (or cell-free) DNA in a blood sample.

The methylation turns genes on or off, explains Cleveland Clinic's Klein in his post. "It's like fingerprints and how fingerprints tell the difference between two people," he wrote. "The methylation patterns are fingerprints that are characteristic of each kind of cancer. They look one way for lung cancer and different for colon cancer." 

The test returns one of two possible results: either "positive, cancer signal detected" or "negative, no cancer signal detected."

According to the company, when a cancer signal is detected, the Galleri test predicts the cancer signal origin "with high accuracy to help guide the next steps to diagnosis."

However, one problem for clinical practice is all the follow-up tests an individual may undergo if their test comes back positive, said Sameek Roychowdhury, MD, PhD, oncologist with Ohio State University Comprehensive Cancer Center, Columbus.

"Not everybody will have an 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," Roychowdhury told Medscape Medical News.

In a large-scale validation study, the Galleri test had a specificity of 99.5% (false-positive rate of 0.5%), meaning in roughly 200 people tested without cancer, only one person received a false-positive result (ie "cancer signal detected" when cancer is not present).

The overall sensitivity of the test for any stage of cancer was 51.5%, although it was higher for later-stage cancers (77% for stage III and 90.1% for stage IV) and lower for early-stage cancers (16.8% for stage I and 40.4% for stage II).

Exacerbate Health Disparities?

In Rebbeck's view, the characteristics of the test are still "relatively poor for detecting very early cancers, so it will need additional tweaking before it really achieves the goal of multi-cancer EARLY detection," he told Medscape Medical News.

Venstrom acknowledges that the test is "not perfect yet" and says the company will continue to update and improve its performance. "We have some new data coming out in September," he said.

Clinical data are being accumulated in the United Kingdom, where the Galleri test is being investigated in a large trial run the by National Health Service (NHS). The company recently announced that the enrollment of 140,000 healthy cancer-free volunteers aged 50-77 into this trial has now been completed, and claimed this the largest-ever study of a multi-cancer early detection test.

Roychowdhury said he would encourage anyone interested in the test to join a clinical trial.

Another expert approached for comment last year, when GRAIL first started marketing the test, was in agreement. This test should be viewed as one that is still under clinical investigation, commented William Grady, MD, a member of the Clinical Research Division and Public Health Sciences Division at the Fred Hutchinson Cancer Research Center, Seattle, Washington.

"The Galleri test is still unproven in the clinical care setting and…I am concerned that many of the results will be false-positives and will cause many unnecessary follow-up tests and imaging studies as well anxiety in the people getting the test done," Grady told Medscape Medical News at the time.

Rebbeck said another issue that needs to be addressed is whether all populations will have access and benefit from these types of blood tests to screen for cancer, given that they are expensive. 

"There is a great danger — as we have seen with many other technological innovations — that the wealthy and connected benefit, but the majority of the population, and particularly those who are underserved, do not," Rebbeck said.

"As a result, health disparities are created or exacerbated. This is something that needs to be addressed so that the future use of these tests will provide equitable benefits," he added.

Rebbeck and Roychowdhury have reported no relevant financial relationships. Venstrom is an employee of GRAIL.

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