FDA Evaluates Grail's Galleri Blood Test for Multi-Cancer Detection

A single blood test that could detect up to 50 types of cancer is under FDA review, with potential approval in 2025—but scientists remain divided on its true value.

The U.S. Food and Drug Administration (FDA) is evaluating Galleri, a blood test developed by Grail that is designed to detect DNA and other markers for up to 50 types of cancer from a single sample. If approved, potentially in 2025, the test could become more broadly available and eligible for Medicare coverage. This review occurs amid ongoing scientific debate regarding the efficacy, limitations, and appropriate use of multi-cancer early detection (MCED) tests.

Test Overview and Regulatory Status

Galleri, and a similar test called Cancerguard by Exact Sciences, are currently available under a special FDA designation. Full FDA approval would enable insurance coverage for the tests. Grail has set a retail price of $950 for Galleri; Cancerguard costs $659. Congress passed legislation in February allowing Medicare to reimburse multi-cancer detection tests starting in 2028.

According to Grail, Galleri is intended to be used alongside, not replace, existing screening tests such as mammography and colonoscopy. Grail's Megan Hall stated that the test is not diagnostic; positive results require follow-up exams. The test provides a "cancer signal origin prediction" to guide physicians.

Clinical Trial Data

Grail is conducting two large-scale studies:

• One with over 142,000 participants in the UK through the National Health Service (NHS)
• Another with 35,000 participants in North America (Pathfinder 2)

The NHS study did not meet its primary goal of reducing late-stage cancer incidence over time. The results indicated that the test did not achieve a statistically significant reduction in advanced-stage cancer diagnoses when used alongside existing screening programs.

Combined data from both studies showed a 26% reduction in Stage IV cancers (specifically pancreatic, liver, lung, and gastric) in the third year.

Scientific Basis and Evaluation Metrics

The science behind these tests, known as 'liquid biopsy,' analyzes markers of cancer, such as DNA fragments shed by cancer cells, detectable in bodily fluids. This technology is already used to monitor cancer progression and guide treatment decisions. However, detecting early-stage cancer is more challenging due to the low concentration of tumor DNA in the blood.

Systematic reviews suggest MCED tests have:

• High specificity (96–99.5%) — meaning they correctly identify most people without cancer
• Variable sensitivity (30–80%) — meaning they may miss a significant proportion of cancer cases

A study of the CancerSEEK test in women aged 65–75 detected only 26 out of 96 diagnosed cancers, while correctly ruling out cancer in 98.9% of those without the disease.

Expert Perspectives

Oncologists view blood-based testing as a promising tool for early detection and monitoring. Lung cancer specialist Jonathan Goldman noted that blood tests already inform treatment decisions and monitoring for cancer recurrence. He predicted future tests might predict cancer risk years in advance.

The American Cancer Society's Arif Kamal stated that many companies are developing similar tests, competing on sensitivity and accuracy. The technology is considered sound, with the main question being the speed of evolution.

Some researchers express caution, highlighting that these tests may fail to detect many early cancers. Concerns include the potential for false-positive results leading to anxiety and unnecessary invasive follow-up procedures, and questions regarding whether the benefits outweigh the downsides given current data.

Eric Topol, a physician-researcher, criticized promoting these tests with the current data.

Current Cancer Screening Landscape

Cancer is a leading cause of death globally, with early detection generally leading to less invasive treatments and better survival rates. Most cancer deaths follow late-stage diagnoses. Existing screening programs (e.g., mammography, colonoscopy) are effective but have limitations in uptake and coverage for many cancer types. Preventive screening in the U.S. detects only 14% of diagnosed cancers. Approximately 40 MCED tests are in development or on sale, but few have undergone randomized controlled trials.

Potential Applications and Limitations

Despite current limitations, these tests may prove beneficial for specific high-risk groups, such as individuals with strong family histories of cancer or inherited genetic mutations. The tests also demonstrate utility in monitoring cancer recurrence after treatment and assisting in the selection of personalized treatments.

Unlike established screening methods, which have decades of evidence demonstrating their ability to reduce cancer deaths, the long-term impact of MCED blood tests on mortality rates in healthy populations remains unproven. The high development and purchase costs of these tests raise concerns about resource allocation, with potential for funds to be diverted from proven public health measures.

Guidance for Individuals

Individuals are advised to consider several points regarding these technologies:

• When invited to participate in a clinical trial for a new cancer blood test, it is important to understand the study's objectives and existing knowledge.
• For privately offered tests, individuals should inquire about result interpretation, post-test support, and the likelihood of the test meaningfully altering care.

Persistent symptoms such as a new lump, unexplained bleeding, a prolonged cough, weight loss, or changes in bowel habits for several weeks warrant a consultation with a physician, even if a previous test result was normal.