A blood sample tube for Galleri blood test for the early diagnosis of multi-cancer (more than 50 types of cancer). While the concept of finding cancer through a simple draw is compelling, high rates of false alarms and missed cancers mea… … More
This year’s Super Bowl Hims & Hers commercial had an advertisement for a “blood test for cancer.” The test is called Galleri, and it retails for $949. On its face, Galleri is compelling: easy and potentially lifesaving. Is it time to run out and get one? Before you do so, ask two questions: “Does it work?” and “Will it help me live a longer, healthier life?” Galleri can be ordered by a doctor or by booking a visit on the Hims & Hers telehealth platform. It analyzes cell-free DNA in the blood, searching for methylation patterns that serve as a fingerprint of cancer.
Getting tested is simple. You buy the test online, go to a testing center for a blood draw and get results in about two weeks. The report states either “cancer signal detected” or “no cancer signal detected.” In real-world use, about 1 in 100 people get a positive signal. For positives, the test predicts a likely tissue of origin — like the pancreas or colon — guiding the subsequent search for cancer.
The manufacturer, GRAIL, recommends Galleri for adults with an elevated cancer risk, such as those 50 or older or people with risk factors like smoking, a personal or family history of cancer, obesity or a genetic predisposition. It’s important to note that the test’s performance and value have not been rigorously studied for each of these groups. The test is not intended for people already in cancer treatment.
Back to the questions around whether to get tested. Today’s evidence-based answer is that multi-cancer early detection tests like Galleri are promising, innovative technologies. Yet for most people, the downsides and uncertainties likely outweigh the potential benefits.
scientific reality.
The first problem is that it misses early cancers, especially ones that are most important to catch. A screening test is most valuable when it finds cancers early, when treatment is most likely to be curative. Yet Galleri’s sensitivity is much higher for later-stage cancers. In a validation study, the sensitivity was only 16.8% for Stage I cancers (very early), jumping to over 90% for Stage IV disease (late stage).
The second issue is a significant false-positive problem. Galleri’s specificity is about 99%. This sounds like great performance. Yet when screening a large, mostly healthy population, even a highly specific test generates a substantial number of false alarms.
In the PATHFINDER study, 62% of positive results were false positives where no cancer was found after an extensive workup. This means most people with a “cancer signal detected” result did not actually have cancer.
For patients, a positive test can trigger what clinicians call a “diagnostic odyssey.” This involves multiple tests — CT, MRI or other scans and sometimes invasive procedures like endoscopy or biopsy, taking on average six months. This time can be filled with appointments, substantial out-of-pocket costs and anxiety, even when no cancer is found.
Finally, a negative Galleri test can be dangerously reassuring. It does not give you a clean bill of health. In PATHFINDER, 71% of the cancers diagnosed during the study were found not by Galleri, but rather through standard screening or symptoms.
A false sense of security could lead patients to delay proven screenings or ignore early symptoms. Importantly, a negative Galleri test does not substitute for guideline-recommended screenings like colonoscopy, mammography or lung cancer CT scans.
Does Galleri Save Lives?
In individual cases, the answer can be yes. Imagine a 55-year-old who gets a Galleri test showing a signal likely from the stomach. An endoscopy then finds an early, treatable gastric cancer. For that person, the test was lifesaving.
In real-world use, a majority of cancers detected by Galleri are those without recommended population-level screenings like stomach, pancreatic or ovarian cancer. This is the test’s most interesting potential. However, because its sensitivity is poorest in early cancer stages, we don’t know if it can reliably shift diagnoses early enough to change population-level outcomes.
A critical issue is that no randomized controlled trial has shown that Galleri testing, on average, reduces cancer mortality. Medicine has a long history of screening tests that detect disease without improving survival, sometimes causing harm through overdiagnosis and overtreatment.
However, large, definitive trials like the U.K.’s NHS-Galleri study (150,000 participants) are underway to answer the mortality question.
Galleri Creates New Problems for Doctors and Patients
A vexing new problem is what’s called the “the diagnostic black hole.” What is a clinician to do when Galleri signals cancer, but CT scans, MRIs, PET scans and endoscopic testing find absolutely nothing? There is no standard protocol for how long or how aggressively to continue searching. This can leave patients in a protracted state of uncertainty.
Furthermore, there is a risk of overdiagnosis, where the test detects a slow-growing, indolent cancer that would never have caused harm in a person’s lifetime, leading to unnecessary treatments, side effects and psychological burden.
Finally, the economics of the test threaten to widen existing healthcare disparities. At $949 out-of-pocket, Galleri is a product for those who have disposable income and access to unproven testing, while proven, life-saving screenings remain underutilized in underserved communities.
Given the performance and complexities, it’s not surprising that no major professional medical society recommends multi-cancer early detection tests for population screening. The stance from organized medicine is that these tests require rigorous validation in ongoing trials and should not be presented to patients as a standard of care.
Considerations For People Who Choose A Galleri Test
Despite the significant caveats, some patients will choose to take the test, particularly those who want to know everything possible about their health, no matter how uncertain the information. Some clinicians, particularly those practicing in concierge or direct-pay models, may also recommend it.
For patients who ultimately choose to get a Galleri test, a thorough, pre-test discussion with a doctor is a must. The conversation should directly present the statistics, including the risks of false negatives and false positives. Critically, the patient and doctor should establish a clear plan for the stressful and costly diagnostic journey that will follow a positive result.
Beyond Galleri: Future Of Multi-Cancer Early Detection
The potential of novel cancer screening tests represent an exciting scientific frontier in medicine. The vision of intercepting dozens of deadly cancers with a simple blood draw is compelling. Yet, the science behind the current approaches to achieving this vision fall short. Ultimately, tests require rigorous validation that demonstrate a net benefit to patients. Future versions of blood-based test for multi-cancer early detection may ultimately prove more accurate.
Until that happens, it’s time to think about cancer prevention beyond tests like Galleri. The most powerful tools for reducing cancer risk are less glamorous, yet they are proven, often covered by insurance and universally applicable. Stay scrupulously up-to-date on guideline-recommended screenings you are eligible for, stop smoking, maintain a healthy weight, limit alcohol and never ignore persistent symptoms.