Imagine detecting multiple cancers through a simple blood draw — that’s the potential of the Galleri multi-cancer early detection (MCED) test, developed by GRAIL, Inc.
The test examines cell-free DNA (cfDNA), which are tiny fragments of genetic material released by dying cells, including cancer cells, into the bloodstream. By analysing DNA methylation patterns, scientists can distinguish between normal and malignant cells and even estimate the likely tissue of origin.[1]
Unlike conventional screenings such as mammography or colonoscopy, which focus on specific organs, Galleri aims to detect multiple cancers at once, including those without established early screening tools, such as pancreatic, ovarian, and oesophageal cancers.[2]
Findings from GRAIL’s PATHFINDER 2 study, a large clinical trial involving thousands of adults aged 50 years and older, have been encouraging. According to PR Newswire (2025), the Galleri test showed a positive predictive value (PPV) of 61.6%, indicating that nearly six out of ten participants with a “cancer signal detected” were confirmed to have cancer after diagnostic evaluation. The test also demonstrated 99.6% specificity, suggesting a very low false-positive rate.
More importantly, over half (53.5%) of cancers detected were in early stages (Stage I or II), when treatment outcomes are typically more favourable. When Galleri was used alongside U.S. Preventive Services Task Force (USPSTF)–recommended screenings, the overall number of cancers identified reportedly increased more than sevenfold.[3]
These results highlight the potential of multi-cancer blood tests to complement existing screening programs by identifying cancers that often go unnoticed until later stages.
While the early data are promising, experts advise a measured interpretation. Most of the evidence so far comes from company-sponsored studies, and peer-reviewed, independent verification is still limited.[4]
Crucially, no large-scale trial has yet demonstrated that using the Galleri test leads to a reduction in cancer-related deaths, which remains the gold standard for evaluating any screening tool. Detecting cancer early does not always guarantee better survival outcomes — especially if the cancer is slow-growing or unlikely to cause harm.[4]
Furthermore, the sensitivity of the test—its ability to correctly detect those who actually have cancer—varies depending on the type and stage. Some cancers may still escape detection, while others may be identified unnecessarily, raising concerns about over-diagnosis and overtreatment.
Health experts emphasize that while Galleri represents an exciting step forward, its role should currently be viewed as experimental and complementary, not as a substitute for standard screening.[2,5]
Both GRAIL and public health authorities agree that Galleri is not intended to replace existing screening methods but to augment them. For instance, the U.S. Preventive Services Task Force (2023) continues to recommend proven, population-based screening tests such as mammography for breast cancer, colonoscopy for colorectal cancer, and low-dose CT for lung cancer.[6]
Galleri may serve as an additional layer of detection, particularly for individuals at higher risk of developing cancers without established screening protocols.[2]
The concept of detecting dozens of cancers from one blood sample marks a major advancement in oncology. If future peer-reviewed studies confirm that the test improves survival and proves cost-effective, it could redefine early cancer detection and prevention globally.
Until then, oncologists recommend balanced optimism — embracing technological progress while insisting on rigorous, transparent validation. Traditional cancer screening and lifestyle-based prevention remain the most reliable tools for reducing cancer mortality today.
1. Galleri Official Website. “What Is Galleri?” Accessed October 2025.
2. BMJ Group. “New Evidence Casts Doubt on a Much-Hyped Blood Test for Early Cancer Detection.” BMJ Group, 2025.
3. U.S. Preventive Services Task Force. “A, B, C Grade Recommendations, Cancer Screenings.” Accessed October 2023.
(Rh/Eth/SS/MSM)
Edited by M Subha Maheswari
