A large-scale study of a multi-cancer blood test found it failed to meet its primary goal of catching cancers before they reach advanced stages, yet the results reveal a more nuanced picture than a simple pass or fail. Researchers analyzing the Galleri test, which screens for 12 different cancer types from a single blood sample, discovered it did not significantly reduce stage III or IV cancer diagnoses in over 142,000 participants from the UK's National Health Service.

What Did the Study Actually Find?

The NHS-Galleri trial, presented at the American Society of Clinical Oncology (ASCO) Annual Meeting in 2026, compared outcomes between people who received the Galleri test and a control group over a median follow-up period of 17 months. While the intervention group did not show a significant reduction in late-stage cancers overall, the data revealed some encouraging findings when researchers looked more closely at the results.

When examining stage IV cancers specifically, the Galleri test showed a 14% reduction in diagnoses compared to the control group, with 342 cases detected in the screened group versus 397 in the control group. Additionally, the test identified 16% more stage I and II cancers in the screened population, catching 647 early-stage cancers compared to 559 in the control group.

The largest improvements in early detection occurred in three cancer types. Esophageal cancer detection increased by 92%, ovarian cancer by 100%, and myeloma or plasma cell neoplasms by 118% among those who received the Galleri test.

How Accurate Is the Blood Test?

Across three screening rounds, the Galleri test demonstrated what researchers described as "robust" performance metrics. The test correctly identified cancer signals 92.5% of the time when a cancer was present, had a positive predictive value of 52%, and a negative predictive value of 99.92%. This means if the test came back negative, patients could be highly confident they did not have one of the screened cancers.

Beyond the primary endpoint, the screened group experienced additional benefits. Members of the intervention group had a 21% reduction in clinically detected cancers and a 25% reduction in emergency presentation diagnoses, meaning fewer people discovered their cancer through urgent hospital visits rather than planned screening.

"It is an oversimplification to think of this trial as either positive or negative. There is more information from which we must learn," said Charles Swanton, MD, PhD, of the Francis Crick Institute and University College London Cancer Institute.

Charles Swanton, MD, PhD, Francis Crick Institute and University College London Cancer Institute

Why Does This Matter for Cancer Screening?

The significance of this research lies in addressing a major gap in cancer care. According to researchers, approximately 70% of cancer deaths in the United States involve cancer types that currently have no guideline-recommended screening program. The Galleri test was designed to address this gap by screening for 12 cancer types simultaneously, including colorectal, pancreatic, stomach, lung, head and neck, liver, bile duct, esophageal, anal, ovarian, bladder cancers, and blood cancers like lymphoma and myeloma.

The trial included 142,826 individuals aged 50 to 77 years from England who had not received a cancer diagnosis or treatment in the previous three years. Roughly half received the Galleri test, while the other half served as a control group with their blood samples stored for comparison.

Steps to Understanding Your Cancer Screening Options

• Know Your Risk Factors: Age, family history, lifestyle factors like smoking, and personal health conditions all influence which cancers you should screen for and when screening should begin.
• Discuss Guideline-Recommended Screening: Talk with your doctor about established screening programs for colorectal cancer, prostate cancer, and other cancers with proven early detection benefits in your age group.
• Ask About Emerging Tests: If you're interested in multi-cancer blood tests like Galleri, discuss with your healthcare provider whether the test is appropriate for you, what it can and cannot detect, and how results would be managed.
• Understand Test Limitations: No screening test catches all cancers, and some tests may detect cancers that wouldn't have caused harm. Your doctor can help you weigh benefits and risks.

What About Vitamin B12 and Cancer Risk?

While screening technology advances, researchers continue investigating other potential cancer warning signs. Some studies have found lower vitamin B12 levels in people with certain cancers, including breast, cervical, liver, stomach, and colorectal cancers. However, experts emphasize that a B12 deficiency is not considered a sign of cancer itself.

The connection between B12 and cancer is complex. Cancers that start in the digestive system often affect how the stomach and intestines work, which can contribute to B12 deficiency rather than the deficiency causing cancer. Additionally, cancer treatments like chemotherapy and radiation therapy can damage the digestive tract and lower B12 levels.

"Any micronutrient deficiency is going to affect your body. There could be a link between B12 and cancer, but we don't have that definitive answer yet," explained Patty McDonnell, RD, CSO, CD, FAND, a clinical oncology nutrition advisor at Fred Hutch Cancer Center.

Patty McDonnell, RD, CSO, CD, FAND, Clinical Oncology Nutrition Advisor at Fred Hutch Cancer Center

Vitamin B12 supports the body in several critical ways. It helps form red blood cells, produces cellular DNA, and keeps nerve cells healthy. The body cannot make B12 on its own; people must obtain it from foods like fish, seafood, meat, poultry, milk, cheese, and yogurt, or from fortified foods and supplements.

If you experience symptoms of B12 deficiency such as anemia, fatigue, memory problems, balance issues, an inflamed tongue, or numbness and tingling in the hands and feet, talk with your healthcare provider about testing. A simple blood test can diagnose a deficiency, and treatment options range from dietary changes to supplements taken under the tongue, inhaled through the nose, or injected into muscle.

"More research is needed to learn whether and how vitamin B12 is connected to cancer. If you have concerns about your B12 levels, talk with a registered dietitian or your healthcare provider," noted Heather Greenlee, ND, PhD, MPH, an American Society of Clinical Oncology expert and medical director of the Integrative Medicine Program at Fred Hutch.

Heather Greenlee, ND, PhD, MPH, American Society of Clinical Oncology Expert and Medical Director of the Integrative Medicine Program at Fred Hutch

The bottom line: while new screening technologies like the Galleri test offer promise in detecting some cancers earlier, they work best alongside established screening programs and conversations with your healthcare team about your individual risk factors and health goals.