Early Cancer Detection Tests
Multi-cancer early detection tests are transforming screening. Learn about liquid biopsies, circulating tumor DNA, and which approaches are supported by evidence.
Key Takeaways
- →Standard screening exists for only 5 cancer types (breast, cervical, colorectal, lung, prostate) — leaving the majority of cancers without screening options.
- →Multi-cancer early detection (MCED) tests like GRAIL Galleri use circulating cell-free DNA to screen for 50+ cancer types from a single blood draw.
- →MCED tests are best at detecting later-stage cancers and have lower sensitivity for stage I disease.
- →A positive MCED result requires confirmatory diagnostic imaging — it is a screening tool, not a diagnostic tool.
Cancer remains the second leading cause of death globally. Early detection dramatically improves survival for most cancer types — yet standard screening guidelines only cover a handful of common cancers. The emergence of liquid biopsy technology and multi-cancer early detection (MCED) tests represents a potential paradigm shift: the ability to screen for dozens of cancer types from a single blood draw.
Standard Cancer Screening
Current evidence-based screening recommendations from the US Preventive Services Task Force (USPSTF) and major cancer organizations cover five cancers:
- •Breast cancer — Mammography every 1–2 years for women 40–74 (USPSTF). MRI screening recommended for high-risk individuals (NCCN).
- •Cervical cancer — Pap smear and/or HPV testing every 3–5 years for women 21–65.
- •Colorectal cancer — Colonoscopy every 10 years or stool-based testing (FIT) annually starting at age 45.
- •Lung cancer — Low-dose CT annually for adults 50–80 with 20+ pack-year smoking history.
- •Prostate cancer — PSA testing is individualized. The American Cancer Society recommends informed decision-making starting at age 50 (or 45 for high-risk men).
The screening gap
Approximately 70% of cancer deaths occur from cancer types for which no routine screening exists — including pancreatic, ovarian, liver, stomach, and brain cancers. This is the gap that MCED tests aim to fill.
Multi-Cancer Early Detection (MCED) Tests
MCED tests analyze cell-free DNA (cfDNA) shed by tumors into the bloodstream. By detecting cancer-specific DNA methylation patterns, these tests can identify a cancer signal and predict the tissue of origin. GRAIL Galleri is the first commercially available MCED test, capable of screening for over 50 cancer types.
GRAIL Galleri: What the Evidence Shows
The PATHFINDER study (2022, Lancet) enrolled over 6,600 adults aged 50+ and found that Galleri detected cancer signals in 1.4% of participants. Of those with a cancer signal, 38% were confirmed to have cancer. The test had a false-positive rate of approximately 0.5%. Sensitivity varied by stage: roughly 17% for stage I, 40% for stage II, 77% for stage III, and 90% for stage IV cancers. The test was strongest for cancers without existing screening tests.
Important limitations
MCED tests are not a replacement for standard cancer screening (mammography, colonoscopy, etc.). They are a supplementary tool. Sensitivity for stage I cancers is still relatively low, meaning a negative result does not rule out early-stage cancer. The long-term impact of MCED screening on cancer mortality has not yet been established in randomized controlled trials — the NHS-Galleri trial (140,000 participants) is ongoing.
Other Liquid Biopsy Applications
- •Circulating tumor DNA (ctDNA) monitoring — Used primarily in diagnosed cancer patients to track treatment response, detect minimal residual disease after surgery, and identify resistance mutations. Companies like Guardant Health and Foundation Medicine offer these tests.
- •PSA refinements — The 4Kscore and Stockholm3 tests combine multiple biomarkers to improve prostate cancer detection and reduce unnecessary biopsies.
- •CancerSEEK (Exact Sciences) — Another MCED platform under development that combines cfDNA with protein biomarkers.
Who Should Consider MCED Testing
MCED testing is most commonly considered by adults over 50, those with strong family histories of cancer, or individuals seeking comprehensive screening beyond standard guidelines. Given the current sensitivity limitations for early-stage disease, MCED tests should complement — not replace — established screening protocols. Discuss with your physician whether adding MCED testing is appropriate for your risk profile.