What To Know About Galleri, the Cancer-detecting Blood Test

Find out what this test can and can't do—and who is eligible to get it.

Research has found that cancer is one of the leading causes of death in the United States.

While many people often live after having cancer and go into remission—thanks to ever-evolving medical treatments—others are still diagnosed too late for treatment to be effective. However, Galleri may be part of the solution for detecting over 50 types of cancers before they reach later stages.

Galleri is a multi-cancer, early-detection blood test manufactured by the company GRAIL. Biotechnology company Illumina Inc. announced the formation of GRAIL in 2016.

The reason for forming the company was to create a pan-cancer screening test to help detect early signs of cancer in asymptomatic patients—something that could "decrease cancer mortality," according to a press release.

In June 2021, GRAIL announced that Galleri was available nationwide as a prescription-only cancer screening test. The announcement was the culmination of years of research backed by notable institutions like the Mayo Clinic, Cleveland Clinic, Dana Farber Cancer Institute, and more.

Here's what you need to know about the science behind the test, what it can—and can't—tell you about your health, and who it can benefit.

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How Does Galleri Work?

GRAIL touted the early cancer-detection test—which would later be named Galleri—as a "simple blood test." But the science behind that simple test is quite complex.

The Biology Behind the Test

Galleri detects cell-free DNA (cfDNA), from tumors, that may be in the blood and show if cancer exists. The test uses DNA sequencing to examine over 100,000 gene areas in a person's DNA.

What Is DNA Sequencing?

DNA sequencing is a method used in a laboratory to determine how the bases in a molecule of DNA are in place, one after the other. By knowing the sequence, scientists can figure out how genes function.

Cancer is when cells being to grow out of control and find their way into other areas of the body. Compared to normal cells, cancerous cells will do things such as:

  • Grow without the body telling them to do so
  • Ignore body signals telling them to stop growing
  • Hide from or trick the immune system

But cancer is also a disease of the genome, or all the genetic information of an organism, made up of DNA. And nearly all of the cells in your body have the same DNA.

But unlike the DNA in healthy cells, the DNA in cancer cells carries cancer-specific signals; tumors shed this DNA into the blood. So, multi-cancer early detection testing looks at blood samples for DNA fragments and their cancer-specific signals. The testing can identify cancer and where cancer signals originated in the body.

The Process for Doing the Test

The Galleri test requires a prescription from a licensed healthcare provider—telemedicine or otherwise—who can request a testing kit on your behalf. Depending on state prescribing laws, the prescribing providers might be:

  • Physicians
  • Nurse practitioners
  • Physician assistants

They may order it electronically through Galleri's provider portal or complete a test requisition form available on their website.

You'll next bring your unopened Galleri specimen collection kit to the provider's office or a lab. At one of those locations, you'll have about 1.5 tablespoons of blood drawn from a vein in your arm. The blood samples will be shipped off to a GRAIL lab for processing, which can take up to 10 business days.

The results go directly to the provider who ordered the test for you. They'll read either "Cancer Signal Not Detected" or "Cancer Signal Detected" with "Top Predicted Cancer Signal Origin(s)," which predicts where cancer may be coming from. The healthcare provider can use these results to order further testing to make a formal diagnosis.

What Galleri Can Tell You About Your Health—and What It Can't

What Galleri Can Do

The United States Preventive Services Task Force (USPSTF) only recommends routine screenings for individuals with risk factors (age, family history, personal history, etc.) when it comes to the following cancers:

  • Colon cancer
  • Breast cancer
  • Cervical cancer
  • Prostate cancer
  • Lung cancer

However, Galleri has been shown to detect more than 50 types of cancer. Some of those cancers—45 to be exact—don't have a recommended screening test available.

The research has been thorough. A group of researchers from Cleveland Clinic, The US Oncology Network, and several other well-respected institutions joined GRAIL to begin the Circulating Cell-Free Genome Atlas study (CCGA). The CCGA study began in 2016 as a three-part study to last up to 5 years overall.

The study as a whole was designed to develop and validate multi‑cancer early detection blood tests in 15,000 subjects with and without a known cancer diagnosis.

The findings from the third substudy, which looked included data from 2016 to 2019, indicated that the tests delivered negative readings to 99.5% of participants who did not have cancer. The tests used a measure known as "specificity" and served up false positives to just 0.5% of participants.

What's more, researchers correctly detected cancer in 51.5% of cancer patients using a measure known as "sensitivity." The blood tests were more likely to detect more advanced cancers. They were most accurate in detecting 12 kinds of cancer for which there are no routine screening tests, including:

  • Liver cancer
  • Head and neck cancer
  • Esophageal cancer (cancer of the esophagus)
  • Pancreatic cancer
  • Ovarian cancer

The separate 2020 PATHFINDER study included 6,629 subjects aged 50 and older who were at higher risks for cancer. Researchers analyzed data based on an earlier version of Galleri and found that the test had detected 29 cancers among 13 cancer types (e.g., lung, small intestine, colon).

About 44.6% of positive test results led to a cancer diagnosis, and nearly 40% of those cancers were stage 1 or stage 2—a good thing because early detection is the pivot for improving cancer outcomes. In 96.3% of cancer cases, Galleri was correct on its first or second indication of where cancer originated from.

And in an analysis of the third substudy for the CCGA study, researchers found that the test picked up cancer signals at high sensitivity—greater than 75%—for several cancers that did not already have screening recommendations in place.

The results seem to be promising. "The test is a step forward and very important for early detection of certain cancers that we don't typically screen for," Christian Rolfo, MD, professor of medicine and associate director for clinical research at the Center of Excellence for Thoracic Oncology at Mount Sinai's Tisch Cancer Institute, told Health.

What Galleri Can't Do

Although Galleri can detect more than 50 types of cancers, that doesn't mean that it can detect all types of cancer.

And while Galleri can help send a healthcare provider in the right direction to conduct further testing and determine whether cancer is present, Dr. Rolfo stressed that these blood tests cannot diagnose cancer and should not replace routine cancer screenings.

Instead, the tests should complement the screenings. "We need to continue to use imaging for diagnostics," said Dr. Rolfo.

GRAIL agreed: "Galleri is not a diagnostic test and is intended to be used as a complement to existing cancer screenings," a GRAIL spokesperson told Health.

Dr. Rolfo's biggest concern is that, on average, the tests pick up just 51.5% of cancers. The test's sensitivity, or ability to detect cancer, varies based on the cancer type and stage, which isn't optimal.

For instance, Galleri was shown to detect just 18.2% of kidney cancers compared to 93.5% of lung cancers. Overall, it picked up 90.1% of stage 4 cancers and only detected an average of 16.8% of stage 1 cancers.

"The test sensitivity is still low among people with stage 1 cancer, which is when we want to detect it since we can detect bigger tumors with imaging," said Dr. Rolfo.

As far as innovation is concerned, Galleri also can't help predict your cancer future. For example, the BRCA genetic blood tests measure your genetic risk of developing cancer at some point.

But Galleri simply tells you whether cancer DNA is currently present in the blood at any given moment—not whether you have a higher risk of developing it in the years to come. "It's still good to have a method to detect certain cancers at an earlier stage," said Dr. Rolfo.

Who Can (And Should) Use the Galleri Test?

Galleri is only recommended for people with heightened cancer risk—being 50 years old or older and having a family history of cancer are both qualifiers.

However, it's best to talk to a healthcare provider about whether you're a candidate for Galleri testing. This is partly because other things can increase your cancer risk, such as:

  • Eating habits
  • Having a weakened immune system (immunosuppression)
  • Lifestyle (e.g., smoking)
  • Genes
  • Cancer-causing substances in the environment (e.g., asbestos)

While GRAIL is careful not to prescribe its tests to any particular demographic, in clinical testing, their researchers enrolled participants who had a history of smoking, documented genetic cancer predisposition, or personal history of cancers that affect the blood, a GRAIL spokesperson told Health.

If this doesn't sound like you, but you've already begun to dial a healthcare provider's number, slow down. "We don't want patients with no known risk factors coming in asking for tests because they are afraid of cancer—we're not there with the technology yet," said Dr. Rolfo.

Other Concerns About the Galleri Test

Of course, there's a chance you might not want this kind of testing in the first place because of how cancer-positive results may make you feel—something GRAIL has already thought about.

"We know that a cancer diagnosis can affect the mental health of patients, families, and their caregivers; feelings of depression, anxiety, and fear are not uncommon," a GRAIL spokesperson wrote via email. "We believe that early detection provides hope and information that patients deserve."

As of December 2022, Galleri costs $949 and isn't covered by insurance. However, you could have the option of using a flexible payment plan, or you may be able to use dollars from your flexible spending account (FSA) or your health savings account (HSA) to pay for it.

And while the tests are available in all 50 states, GRAIL is still working toward approval from the U.S. Food and Drug Administration (FDA).

With the average person undergoing multiple routine screenings as they get older, soon Galleri testing or other modes of early cancer detection could be just as common. The fact remains that early cancer detection can reduce cancer mortality rates, and beating cancer begins with knowing you have it.

A Quick Review

Galleri is a multi-cancer early detection blood test that can detect signals from over 50 types of cancers. Research has found that Galleri may work well alongside other methods in the cancer screening process.

However, the test cannot detect all cancers or predict what future cancers you might develop. Additionally, the Galleri test is only available by prescription and is recommended for individuals with higher cancer risk factors, like age and family history.

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