The Galleri test screens for more than 50 types of cancer from a single blood draw. It covers many cancers that have no standard screening test today, including pancreatic, liver, ovarian, and stomach cancers. The test works by analyzing DNA fragments that tumors shed into the bloodstream, and it can also predict where in the body a cancer signal is coming from.
The Full List of Cancers Galleri Detects
Galleri has demonstrated the ability to detect cancer signals across a wide range of tumor types. The complete list, organized by body system, includes:
- Digestive system: Colon and rectum, stomach, esophagus, small intestine, pancreas (exocrine), gallbladder, liver, appendix, ampulla of Vater
- Bile duct cancers: Intrahepatic, perihilar, and distal bile duct cancers
- Reproductive organs: Ovary, fallopian tube, and primary peritoneum; cervix; uterine carcinoma and sarcoma; vagina; vulva; testis; penis; gestational trophoblastic neoplasms
- Urinary tract: Bladder, kidney, ureter and renal pelvis
- Respiratory and chest: Lung, malignant pleural mesothelioma, larynx
- Head and neck: Oral cavity, nasopharynx, nasal cavity and paranasal sinuses, oropharynx (both HPV-mediated and non-HPV), hypopharynx
- Blood cancers: Leukemia, Hodgkin lymphoma, non-Hodgkin lymphoma, plasma cell myeloma and plasma cell disorders
- Skin: Melanoma, Merkel cell carcinoma
- Soft tissue sarcomas: Abdomen, thoracic organs, head and neck, retroperitoneum, trunk and extremities, plus unusual histologies and sites
- Neuroendocrine tumors: Appendix, colon and rectum, pancreas
- Other: Breast, prostate, bone, adrenal cortical carcinoma, gastrointestinal stromal tumor
That said, the test is not equally good at finding every cancer on this list. It tends to perform less well for slower-growing cancers like many breast and prostate tumors. It is not a substitute for existing screenings like mammography, colonoscopy, or cervical cancer screening.
How the Test Works
Galleri detects cancer through a process that reads chemical tags on DNA fragments floating in your blood. When cells die, including cancer cells, they release bits of their DNA into the bloodstream. These fragments are called cell-free DNA. The test zeroes in on roughly one million specific spots across the genome where chemical tags called methyl groups are either present or absent.
Cancer cells have dramatically different tagging patterns compared to healthy cells. A machine learning algorithm trained on these patterns can distinguish a cancer signal from normal background noise. This approach works better than looking for genetic mutations, partly because methylation patterns are far more widespread across the genome and partly because they naturally reflect what type of tissue the DNA came from. That tissue-specific signature is what allows the test to predict not just that cancer is present, but where it likely originated.
How Accurate the Test Is by Cancer Stage
Galleri’s ability to detect cancer depends heavily on how advanced the disease is. Overall sensitivity across all cancer types is about 51.5%. Broken down by stage, the numbers tell a clearer story: Stage I cancers are detected about 16.8% of the time, Stage II about 40.4%, Stage III about 77%, and Stage IV about 90.1%. For early-stage cancers specifically (Stage I and II combined), overall sensitivity is roughly 27.5%, though this improves to about 52.8% for a subset of 12 cancers the test’s developers identified as having high unmet need, meaning cancers that lack good existing screening options.
The test’s specificity is 99.5%, which means that out of every 1,000 people without cancer, roughly 995 will correctly receive a “no cancer signal detected” result. The false-positive rate of 0.5% sounds small, but in a large screening population it still produces a meaningful number of people who get a positive result without actually having cancer.
What a Positive Result Means
In the PATHFINDER clinical trial, which enrolled over 6,600 participants, a cancer signal was detected in 1.4% of people tested. Of those 92 positive results, 35 (38%) turned out to be true cancers and 57 (62%) were false positives. The positive predictive value, or the chance that a positive result actually means cancer, was 38% in that study.
When the test does detect a real cancer, it also predicts the most likely organ of origin. For blood cancers, this prediction is extremely accurate: 99% for lymphoid cancers and 100% for plasma cell cancers in validated cases. This prediction helps guide doctors toward the right follow-up imaging and testing rather than searching blindly.
What Happens After a Positive Result
A positive Galleri result triggers a diagnostic workup that typically involves blood tests, imaging, and sometimes biopsies. In the PATHFINDER trial, most participants with positive results underwent both lab work (around 80 to 88%) and imaging (around 91 to 93%), regardless of whether the result turned out to be a true or false positive.
For people who truly had cancer, reaching a confirmed diagnosis took a median of 57 days and required about three diagnostic tests or procedures. False positives took longer to resolve, with a median of 162 days and about five tests, because ruling cancer out often requires more investigation than confirming it. Few participants in either group needed surgery during the workup.
One concern raised by early clinical experience is inconsistency in follow-up care. In some cases, patients received inappropriate studies for the type of cancer suggested or were incorrectly reassured that no further testing was needed. Standardized follow-up protocols are still being developed, so the quality of your workup depends partly on how familiar your provider is with interpreting these results.
Who the Test Is For
Galleri is recommended for adults with an elevated risk of cancer, particularly those aged 50 and older. It is not intended for people who are 21 or younger, those who are pregnant, or anyone currently undergoing active cancer treatment. The test is designed to complement, not replace, standard cancer screenings.
TRICARE now covers the Galleri test for beneficiaries aged 50 and older who have an elevated cancer risk, though cost-sharing applies. Medicare does not cover it. For most people, the test remains an out-of-pocket expense unless their employer or health plan has specifically added coverage. If you’re on TRICARE for Life, expect to pay the annual deductible and applicable cost share since Medicare won’t pick up its portion.
Key Limitations to Understand
A negative Galleri result does not mean you are cancer-free. The test misses the majority of Stage I cancers and has lower sensitivity for slow-growing tumors like many breast and prostate cancers. These are cancers that existing screening tools, like mammograms and PSA testing, are already designed to catch. Galleri’s greatest value is in detecting cancers that currently have no routine screening method, particularly aggressive cancers of the pancreas, ovary, liver, and blood.
The false-positive rate, while low at 0.5%, can lead to months of additional testing, imaging, and anxiety before a cancer diagnosis is ruled out. In the PATHFINDER trial, false-positive cases took over five months on average to fully resolve. For people considering the test, understanding that a positive result is more likely to be a false alarm than a confirmed cancer is important context.