Multi-Cancer Early Detection (MCED) Blood Tests: Performance Limitations and Clinical Utility
Multi-cancer early detection (MCED) blood tests aim to identify signals from multiple cancer types in a single sample. These tests primarily analyze cell-free DNA methylation patterns or other circulating biomarkers. Researchers and companies continue to evaluate their performance in large studies. However, questions remain about their real-world impact.
Performance of Current MCED Tests
Current MCED tests demonstrate high specificity, typically ranging from 99.5% to 99.9%. As a result, false-positive rates stay low, often around 0.4% to 0.5%. Positive predictive values (PPV) generally fall between 50% and 77% across major studies. For example, the Galleri test showed a PPV of about 60% to 77% in PATHFINDER 2 and related analyses. In addition, cancer signal origin (CSO) prediction accuracy reaches 91% to 94%. This feature helps direct subsequent diagnostic testing toward the most likely cancer site.
Overall episode sensitivity remains moderate, usually between 30% and 40% in prospective screening populations. Sensitivity improves for certain high-mortality cancers and later-stage disease. In one analysis of 12 key cancers, sensitivity reached nearly 70%. Many detected cancers lack recommended standard screening tests. Furthermore, a substantial portion of MCED-detected cases appear at stage I or II in some datasets. Negative predictive values stay high, above 98%. Therefore, a negative result carries relatively strong reassurance in low-prevalence settings.
Limitations and Challenges
Sensitivity drops notably for early-stage cancers and for certain tumor types such as breast or prostate cancer in some reports. Consequently, many cancers still go undetected. The large NHS-Galleri randomized trial failed to meet its primary endpoint of reducing the incidence of stage III or IV cancers after three screening rounds. Incidence rate ratios showed no significant difference between the intervention and control groups. Meanwhile, concerns about overdiagnosis persist because some detected cancers may never progress to cause harm.
False-positive results, although uncommon, can trigger invasive procedures, imaging, and anxiety. Lead-time bias and verification bias also complicate interpretation of earlier detection claims. No completed randomized trial has yet shown a reduction in cancer-specific or overall mortality. In addition, the tests remain expensive (around $949 for Galleri) and are not covered by most insurance plans for routine screening. Systematic reviews conclude that current evidence is insufficient to support broad population use due to limited outcome data and study design issues.
Clinical Utility and Current Status
MCED tests are intended as an adjunct to, not a replacement for, established screening methods such as mammography, colonoscopy, and low-dose CT. They may help identify cancers that lack routine screening options and guide more efficient diagnostic workups through CSO prediction. In 2026, an FDA advisory panel voted unanimously in favor of the Galleri test’s safety and supported its benefit-risk profile by a narrower margin, while the vote on effectiveness was split.
Ongoing and future randomized trials, along with longer follow-up, will determine whether earlier detection translates into meaningful clinical benefits such as stage shift or reduced mortality. Overall, MCED blood tests show analytical promise and high specificity, but their clinical utility in reducing cancer deaths remains unproven. Clinicians and patients should continue standard screening and interpret results in the context of individual risk and evolving evidence.