Previous cancer blood test results

In 2021, Grail launched the first multi-cancer early detection test called Galleri. The test analyzes fragments of cell-free DNA shed by tumors in the bloodstream to identify any chemical methylation patterns that could indicate the presence of cancer.

In 2022, Grail released the findings of a trial involving 6,629 patients. At the time, interim data showed that the Galleri test was able to detect cancer signals in 92 participants, with 29 having cancers that were detected by additional tests, such as CT/PET scans and biopsies. Of these participants, 23 were newly diagnosed with cancer, including nine early-stage cases, while six experienced a cancer recurrence.

Then, in October 2025, Grail announced the results of a larger clinical trial called Pathfinder 2 that included nearly 36,000 participants ages 50 and older from the United States and Canada with no clinical suspicion of cancer.

That trial found that the test was able to detect a cancer signal in 216 participants, and of those participants, 133 were diagnosed with cancer. The positive predictive value, or the likelihood of receiving a cancer diagnosis following a positive test result, was 61.6% — much higher than what was found in previous trials (43% to 50%). Of the new cancers detected, over half were in stage I or II, and over two-thirds were in stages I to III.

Newest cancer blood test shows disappointing results

In February, Grail announced the results of another trial that showed fewer encouraging results.  The study enrolled 142,000 healthy adults aged 50 to 77 in Britain and followed them for three years. Participants in the study had their blood drawn three times, each spaced around a year apart. One group of the participants' blood samples were run through Galleri, and those people were referred for medical care if they tested positive.

Grail then compared the group that underwent the Galleri screening with another group that didn't get the test with the goal of finding a 20% reduction in advanced cancers among those who got the test.

Ultimately, the study found that recipients of the Galleri test didn't show a significant reduction in the total number of cancers diagnosed at stage III or IV. In a call with analysts, Grail executives said they were encouraged by other findings that weren't the primary goal of the study, noting a decrease in stage IV cancers and an increase in stage III — a result that could indicate cancers were being found slightly earlier.

"It's absolutely right to say we didn't hit the primary endpoint," said Harpal Kumar, Grail's chief scientific officer. "But what we did see was a very compelling clinical benefit here."

However, experts say the question around these tests isn't whether they can detect cancer but whether they can find cancers early enough to prevent deaths.

The results of Grail's most recent study show Galleri is "not a very good test," said Richard Houlston, who studies cancer genetics at the Institute of Cancer Research in Britain. "This doesn't support rollout within the American healthcare system."

Similarly, Adewole Adamson, a cancer researcher at the University of Texas at Austin's Dell Medical School said the study failed, "end of story."

"If there was a slam dunk result, we would have seen it" given how large the trial was, he added.

Josh Ofman, president of Grail, noted that while the study didn't find a reduction of combined stage III and IV cancers, he did mention it showed a 20% reduction of stage IV cancers, a finding that Dahut said is encouraging.

"My sense is that these tests, if they're abnormal, they're a pretty good sign that you have cancer," he said. "And oftentimes the cancers that they found were cancers that are not routinely screened for such as head and neck cancer and gastric cancers."

"But a negative test does not exclude the fact that you could have cancer, you still need to do other screening tests," Dahut added.

To evaluate a test's effectiveness, it's important to look at both its sensitivity and specificity, according to Badrinath Konety, president of the Allina Health Cancer Institute. Sensitivity shows how well a test identifies disease while specificity shows how well it avoids false positives.

Konety said that Galleri seems to have higher sensitivity for more uncommon cancers but less so for common ones, especially when it's early-stage common cancers like breast and prostate. If a test is positive, patients must still undergo the routine diagnostic procedures.

"If a test is positive this is going to lead to X-rays and biopsies and additional interventions which are not only costly but can add to complications and the suffering of patients, and what if everything turns out to be negative," Konety said.

Konety added that the tests do a good job of finding cancer, but he worries that if someone tests negative for a cancer, the result could create a false sense of complacency, leading them to avoid a traditional screening test.

"Are we going to give people a false sense of comfort?" he said.