New blood tests offering the potential to detect multiple cancers at an early stage are generating excitement, but experts caution that widespread clinical use remains years away. Recent modeling studies suggest these “multicancer early detection” (MCED) tests could reduce late-stage diagnoses by nearly half, yet high false-positive rates and a lack of standardized guidelines currently hinder their adoption.
The Allure of Blood-Based Cancer Screening
The core concept behind liquid biopsies is simple: detect cancer without invasive tissue sampling. Instead of surgically removing a tumor fragment, clinicians can analyze blood for circulating tumor cells, DNA fragments, or other markers released by cancer. This approach offers a less invasive and potentially more comprehensive view of the disease than traditional biopsies, which may only capture a small portion of a tumor’s genetic diversity.
Currently, five FDA-approved liquid biopsy tests exist, each designed for a single cancer type. However, no MCED tests have received formal approval, though some are available as “laboratory-developed tests” (LDTs) in the U.S. and are undergoing trials in Europe, such as the U.K.’s PATHFINDER 2 study examining GRAIL’s Galleri test.
Why Implementation Is Slowing
Despite the promise, several obstacles delay widespread clinical use:
- False Positives: Current MCED tests have unacceptably high false-positive rates. The PATHFINDER 2 trial showed roughly 40% of patients diagnosed with cancer by Galleri were cancer-free, raising unnecessary anxiety and triggering follow-up tests.
- Lack of Standardization: Different tests use varying assays and analyze cancer markers at different stages, making head-to-head comparisons difficult.
- Entrenched Practices: Oncologists have relied on tissue biopsies for decades; shifting diagnostic paradigms requires significant inertia.
- Uncertain Dwell Times: The effectiveness of MCED tests depends on how long cancers remain detectable in early stages, and this varies significantly by cancer type. Some cancers progress too quickly for annual testing to make a difference.
- Confirmation Required: A positive liquid biopsy result still requires tissue confirmation, which adds cost and delay.
The Future Outlook
Experts remain cautiously optimistic. Researchers at Fred Hutch cancer center and Weill Cornell Medicine agree that optimized MCED tests with lower false-positive rates are on the horizon. One promising avenue is analyzing additional cell types (such as immune cells) to improve test specificity. Liquid biopsies may eventually help identify patients who can avoid unnecessary chemotherapy by assessing residual tumor DNA in the blood after surgery.
While current MCED tests are not ready to replace existing diagnostics, ongoing research and standardization efforts could transform cancer screening within the next decade. The key will be reducing false positives, refining cancer dwell time estimates, and integrating these tests into standardized clinical pathways.
